Anti-ILT5 antibodies and ILT5-binding antibody fragments

ABSTRACT

Disclosed herein are antibodies and ILT5-binding fragments thereof that specifically bind to ILT5, e.g., human ILT5 (hILT5), and pharmaceutical compositions comprising such ILT5-binding antibodies and ILT5-binding fragments thereof.

CROSS REFERENCE TO PRIOR APPLICATIONS

This is a U.S. National Phase application under 35 U.S.C. §371 ofInternational Patent Application No. PCT/US2011/021939, filed Jan. 20,2011, and claims the benefit of U.S. Provisional Patent Application No.61/296,791, filed Jan. 20, 2010, both of which are incorporated byreference herein in their entirety. The International Applicationpublished in English on Jul. 28, 2011 as WO 2011/091177 under PCTArticle 21(2).

BACKGROUND

The immune system has evolved multiple mechanisms to preserve immunehomeostasis and protective immunity while sparing “self” from autoimmunedestruction. The initiation of immunity is a tightly controlled processthat relies in part on interplay between inhibitory and activatingreceptors. Immunoglobulin-like transcripts (ILTs), which encompass bothtypes of receptors, are encoded by rapidly evolving genes found in humanand non-human primates. Immunoglobulin-like transcript 5 (“ILT5”) is acell surface molecule that is a member of the immunoglobulin superfamilyand is highly expressed on antigen-presenting cells (APCs), such asimmature dendritic cells and monocytes.

SUMMARY

Disclosed herein are antibodies and ILT5-binding fragments thereof thatspecifically bind to ILT5, e.g., human ILT5 (hILT5), on antigenpresenting cells (APCs), such as for example, monocytes, macrophages andcertain dendritic cells (DC), e.g., myeloid dendritic cells. Alsodisclosed are pharmaceutical compositions comprising ILT5-bindingantibodies and ILT5-binding fragments thereof.

In certain embodiments, compositions provided herein comprise anisolated antibody that binds ILT5 or an ILT5-binding fragment of theantibody, comprising a heavy chain complementarity determining region 1(VH CDR1) comprising or consisting of the amino acid sequence of SEQ IDNO: 4, a heavy chain complementarity determining region 2 (VH CDR2)comprising or consisting of the amino acid sequence of SEQ ID NO: 5, anda heavy chain complementarity determining region 3 (VH CDR3) comprisingor consisting of the amino acid sequence of SEQ ID NO: 6. In certainembodiments, compositions provided herein comprise an isolated antibodythat binds ILT5 or an ILT5-binding fragment of the antibody, orconsisting of a light chain complementarity determining region 1 (VLCDR1) comprising or consisting of the amino acid sequence of SEQ ID NO:7, a light chain complementarity determining region 2 (VL CDR2)comprising or consisting of the amino acid sequence of SEQ ID NO: 8, anda light chain complementarity determining region 3 (VL CDR3) comprisingor consisting of the amino acid sequence of SEQ ID NO: 9.

In certain embodiments, compositions provided herein comprise anisolated antibody that binds ILT5 or an ILT5-binding fragment of theantibody, comprising a heavy chain complementarity determining region 1(VH CDR1) consisting of the amino acid sequence of SEQ ID NO: 4, a heavychain complementarity determining region 2 (VH CDR2) consisting of theamino acid sequence of SEQ ID NO: 5, a heavy chain complementaritydetermining region 3 (VH CDR3) consisting of the amino acid sequence ofSEQ ID NO: 6, a light chain complementarity determining region 1 (VLCDR1) consisting of the amino acid sequence of SEQ ID NO: 7, a lightchain complementarity determining region 2 (VL CDR2) consisting of theamino acid sequence of SEQ ID NO: 8, and a light chain complementaritydetermining region 3 (VL CDR3) consisting of the amino acid sequence ofSEQ ID NO: 9.

In certain embodiments, an isolated antibody that binds ILT5 or anILT5-binding fragment of the antibody comprises at least one humanframework region. For example, the anti-ILT5 antibody or ILT5-bindingfragment can comprise one or more human heavy chain framework regionssuch as, without limitation, one or more human heavy chain frameworkregions from a heavy chain variable region comprising an amino acidsequence selected from the group consisting of the amino acid sequenceof SEQ ID NO: 10, SEQ ID NO: 11, SEQ ID NO: 12, SEQ ID NO: 13, SEQ IDNO: 14, SEQ ID NO: 15, SEQ ID NO: 16, and SEQ ID NO: 17. Additionally oralternatively, the anti-ILT5 antibody or ILT5-binding fragment cancomprise or more human light chain framework regions such as, withoutlimitation, one or more human light chain framework regions from a lightchain variable region comprising an amino acid sequence selected fromthe group consisting of the amino acid sequence of SEQ ID NO: 18, SEQ IDNO: 19, SEQ ID NO: 20, SEQ ID NO: 21, SEQ ID NO: 22, SEQ ID NO: 23, andSEQ ID NO: 24.

In certain embodiments, an isolated antibody that binds ILT5 or anILT5-binding fragment of the antibody comprises a heavy chain constantregion, e.g., an IgG1 constant region, an IgG2 constant region, an IgG3constant region, an IgG4 constant region, an IgA constant region, an IgEconstant region, an IgM constant region, or an IgD constant region. Incertain embodiments, an isolated antibody that binds ILT5 or anILT5-binding fragment of the antibody comprises a heavy chain constantregion comprising the amino acid sequence of SEQ ID NO: 25 or SEQ ID NO:26.

In certain embodiments, an isolated antibody that binds ILT5 or anILT5-binding fragment of the antibody comprises a light chain constantregion, e.g., kappa light chain constant region or a lambda light chainconstant region. In certain embodiments, an isolated antibody that bindsILT5 or an ILT5-binding fragment of the antibody comprises a light chainconstant region comprising the amino acid sequence of SEQ ID NO: 27.

In certain embodiments, an isolated antibody that binds ILT5 or anILT5-binding fragment of the antibody comprises a light chain comprisingthe amino acid sequence of SEQ ID NO: 28. In certain embodiments, anisolated antibody that binds ILT5 or an ILT5-binding fragment of theantibody comprises a heavy chain comprising the amino acid sequence ofSEQ ID NO: 29, SEQ ID NO: 30, SEQ ID NO: 31, or SEQ ID NO: 32. Incertain embodiments, an isolated antibody that binds ILT5 or anILT5-binding fragment of the antibody comprises a light chain comprisingthe amino acid sequence of SEQ ID NO: 28, and further comprises a heavychain comprising the amino acid sequence of SEQ ID NO: 29, SEQ ID NO:30, SEQ ID NO: 31, or SEQ ID NO: 32.

In certain embodiments, an isolated antibody that binds ILT5 or anILT5-binding fragment of the antibody comprises a light chain variableregion comprising the amino acid sequence of SEQ ID NO: 1. In certainembodiments, an isolated antibody that binds ILT5 or an ILT5-bindingfragment of the antibody comprises a heavy chain variable regioncomprising the amino acid sequence of SEQ ID NO: 2 or SEQ ID NO: 3. Incertain embodiments, an isolated antibody that binds ILT5 or anILT5-binding fragment of the antibody comprises a light chain variableregion comprising the amino acid sequence of SEQ ID NO: 1, and furthercomprises a heavy chain variable region comprising the amino acidsequence of SEQ ID NO: 2 or SEQ ID NO: 3.

In certain embodiments, an isolated antibody that binds ILT5 or anILT5-binding fragment of the antibody comprises a polypeptide having1-10 amino acid substitutions, deletions or insertions as compared to apolypeptide selected from the group consisting of a heavy chaincomprising the amino acid sequence of SEQ ID NO: 29, SEQ ID NO: 30, SEQID NO: 31, or SEQ ID NO: 32, a heavy chain variable region comprisingthe amino acid sequence of SEQ ID NO: 2, SEQ ID NO: 3, SEQ ID NO: 10,SEQ ID NO: 11, SEQ ID NO: 12, SEQ ID NO: 13, SEQ ID NO: 14, SEQ ID NO:15, SEQ ID NO: 16, or SEQ ID NO: 17, a heavy chain constant regioncomprising the amino acid sequence of SEQ ID NO: 25 or SEQ ID NO: 26, alight chain comprising the amino acid sequence of SEQ ID NO: 28, a lightchain variable region comprising the amino acid sequence of SEQ ID NO:1, SEQ ID NO: 18, SEQ ID NO: 19, SEQ ID NO: 20, SEQ ID NO: 21, SEQ IDNO: 22, SEQ ID NO: 23, or SEQ ID NO: 24, or a light chain constantregion comprising the amino acid sequence of SEQ ID NO: 27. In certainembodiments, at least one substitution comprises a backmutation to anon-human framework residue.

In certain embodiments, an isolated antibody that binds ILT5 or anILT5-binding fragment of the antibody binds human ILT5. In certainembodiments, an ILT5-binding fragment of an antibody that binds ILT5comprises a Fab fragment, a F(ab′)2 fragment, or a scFv fragment.

Unless otherwise defined, all technical and scientific terms used hereinhave the same meaning as commonly understood by one skilled in the artto which this invention belongs. Methods and materials are describedherein for use in the present invention; other, suitable methods andmaterials known in the art can also be used. The materials, methods, andexamples are illustrative only and not intended to be limiting. Allpublications, patent applications, patents, sequences, database entries,and other references mentioned herein are incorporated by reference intheir entirety. In case of conflict, the present specification,including definitions, will control.

Other features and advantages of the invention will be apparent from thefollowing detailed description and figures, and from the claims.

DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the expression of ILT5 by various hematopoietic subsets inthe form of two-dimensional flow cytometry (FCM) representations calledquantile contour plots (or probability plots). The latter plots show thelevels of two fluorescent parameters (i.e., fluorescent antibodies) onvarious cell subpopulations, quantitate the proportions of cellsdisplaying these parameters, and indicate the frequency of cells presentat each point in the plot. Here, peripheral blood mononuclear cells(PBMCs) from a healthy human donor were stained with the TRX585 antibodyas well as antibodies specific for the indicated cell subset. In FIG.1A, plots depict ILT5 (TRX585) expression by gated CD56⁻CD3⁺CD4⁺ orCD56⁻CD3⁺CD8⁺ T cells. In FIG. 1B, PBMCs were stained as in (A) andsubsequently stained for intracellular Foxp3. Plots show ILT5 expressionby gated CD56⁻CD3⁺CD4⁺Foxp3⁺ or CD56⁻ CD3⁺CD4⁺Foxp3⁻ T cells. FIG. 1Cshows ILT5 expression by CD4⁺, CD8⁺ or CD4⁻CD8⁻ NKT (CD56⁺CD3⁺) cells.FIG. 1D shows ILT5 expression by myeloid (CD11c⁺HLA-DR⁺) andplasmacytoid (CD123⁺BDCA-2⁺) DC cells. FIG. 1E shows expression of ILT5and CD11b by CD33^(hi)CD34⁻, CD33^(hi)CD34^(lo) and CD33^(int)CD34⁻monocyte subsets as well as by CD33^(lo)CD34⁺ myeloid progenitors. FIG.1F shows ILT5 expression by CD33^(hi)CD34^(lo)CD11b⁺CD14⁺ myeloidderived suppressor cells (MDSCs). Percentages of gated cells and meanfluorescence intensity of the ILT5-staining of ILT5⁺ cells are depictedinside and above plots, respectively. Specificity of the ILT5 stainingwas ascertained by staining all of the above cell subsets with a mIgG1isotype control antibody. Data are representative of 4 independentexperiments.

FIG. 2 is a series of bar graphs showing TRX585 antibody-mediatedhyperresponsiveness of allogeneic responder lymphocytes in primary MLRs(mixed lymphocyte reactions). 2×10⁵ PBMCs (responder population)/wellwere cultured with 2×10⁵ mitomycin-treated PBMCs (stimulator population)from an unrelated blood donor in the presence or absence of theindicated amounts of mIgG1 or TRX585 antibodies. Proliferative activityin the MLR was measured at day 3.5 by the incorporation of 1 μCi [³H]TdR(tritiated thymidine) per well to the DNA of replicating cells duringthe last 12-18 hours of the culture. The X axes indicate theconcentration of antibody. The Y axes indicate [³H]TdR uptake. Datashown are representative of several experiments utilizing differentresponder/stimulator pairs and are reported as the mean cpm±standarderror of triplicate wells.

FIG. 3 is a pair of bar graphs showing that pretreatment of peripheralblood monocytes or DCs with soluble TRX585 antibody prior to their usein MLR assays resulted in antibody-mediated enhancement of cellproliferation. DCs or monocytes that were purified from PBMCs wereincubated in the presence or absence of 50 μg/ml mIgG1 isotype controlor TRX585 antibody. Twenty four hours later, precultured DCs andmonocytes were washed to remove unbound antibodies, seeded at 1000 and120,000 cells per well, respectively, and cocultured with 1×10⁵ T cellsfreshly isolated from PBMCs. [³H]thymidine incorporation was measured asdescribed above. Data shown are representative of several experimentsutilizing different responder/stimulator pairs and are reported as themean cpm of triplicate wells. The X axes indicate which antibody wasused. The Y axes indicate [³H]TdR uptake.

FIG. 4 is a pair of bar graphs showing that monovalent but not divalentTRX585 antibody is endowed with stimulatory potential. 2×10⁵ PBMCs/wellwere cultured with 2×10⁵ mitomycin-treated allogeneic PBMCs in thepresence or absence of 10 μg/ml of goat anti-mouse F(ab′)2 fragments andvarious concentrations of soluble TRX585 or mIgG1, as indicated on thefigure. [³H]TdR-incorporation (1 μCi/well) in the last 12-18 hours ofthe cultured was measured at day 3.5. Shown are the mean cpm oftriplicate wells.

FIG. 5 is a pair of bar graphs showing that immobilization of TRX585antibody on plastic abolishes its immunostimulatory potential. 2×10⁵PBMCs/well were cultured with 2×10⁵ mitomycin-treated allogeneic PBMCswith either soluble or tissue culture plate-bound TRX585, which wascoated onto the tissue culture plate well bottoms at the indicatedconcentrations. [³H]TdR-incorporation (1 μCi/well) in the last 12-18hours of the culture was measured at day 3.5. The X axes indicate theconcentration of antibody. The Y axes indicate [³H]TdR uptake. Shown isthe mean cpm of triplicate wells.

FIG. 6 is a series of two dimensional displays called color densityplots (or pseudo-color plots) and bar graphs showing that TRX585 inducesthe proliferation of the majority of T cells and that this proliferationrequires the presence of non-T cells. Color density plots provide thesame information as quantile contour plots. In FIG. 6A, 1×10⁷ PBMCs perml were stained with 1 μM CFSE (carboxyfluorescein succinimidyl ester)in PBS 0.1% BSA for 20 min at 37° C., followed by 2 washes in cold PBS.2×10⁵ CFSE-labeled PBMCs (responder population)/well were cultured with2×10⁵ mitomycin-treated, allogeneic or autologous PBMCs (stimulatorpopulation) in the presence or absence of mIgG1 or TRX585 antibodies (50μg/ml). Three and a half days later, cells were stained with CD4 and CD8antibodies as well as the viability dye, 7-amino-actinomycin D (7AAD).Dilution of the CFSE dye in viable CD4 and CD8 T cells, which isindicative of cell proliferation, was examined by flow cytometry. In theexperiment shown in FIG. 6B, 1×10⁵ T cells purified from PBMCs wereeither cultured alone (upper graph) or mixed with 2×10⁵mitomycin-treated PBMCs (bottom graph), in the presence or absence ofthe indicated amount of mIgG1 isotype control or TRX585 antibody. T cellproliferation was measured at day 3.5 by means of [³H]TdR-incorporationas reported above. In the experiment shown in FIG. 6B, the X axesindicate the concentration of antibody, while the Y axes indicate[³H]TdR uptake. Shown are the mean±standard error cpm of triplicatewells.

FIG. 7 is a series of FCM pseudo-color plots showing that TRX585antibody-induced T cell proliferation is TCR-independent. Respondercells (CD4⁺ and CD8⁺ T cells) as well as stimulator cells (CD4⁻ and CD8⁻cells) were isolated, using a fluorescence-activated cell sorter(FACSAria), from PBMCs that were stained with CD4 and CD8 antibodies aswell as 7AAD (7-aminoactinomycin D). Stimulator cells were inactivatedby mitomycin treatment and subsequently incubated with saturatingamounts of W6/32 (anti-pan-HLA class I) or Tü39 (anti-pan-HLA class II)or no blocking antibody for 30 minutes at 37° C., followed by washes.Responder cells were CFSE-labeled as previously described. 2×10⁵CFSE-labeled responder cells were mixed with 2×10⁵ mitomycin-treatedstimulator cells in the presence or absence of TRX585 antibody (50μg/ml). Three and an half days later, CD4 and CD8 T cell proliferationwas examined by flow cytometry. Plots show the proliferation of CD4⁺ Tcells (left two columns of plots) and CD8⁺ T cells (right two columns ofplots) in the absence of blocking antibody (top row of plots), or in thepresence of pan anti-MHC class I antibody (middle row of plots), and pananti-MHC class II antibody (bottom row of plots). Percentage ofproliferating cells is depicted inside the plots.

FIG. 8 is a series of FCM pseudo-color plots showing the phenotype ofTRX585 antibody-activated T cells. FIG. 8A is a representation of atwo-parameter flow cytometry analysis of CFSE-labeled PBMCs that werecultured for 3.5 days with or without TRX585 antibody (50 μg/ml) andsubsequently stained with CD4, CD8 and CD25 antibodies. FIG. 8B showsNKG2D expression by PBMCs cultured as previously described and stainedwith CD4, CD8 and NKG2D antibodies. The plot on the right hand sidedepicts NKG2D expression by freshly isolated PBMCs. Numbers in plotsindicate the proportion of cells within a given quadrant. Dead cellswere systematically excluded from the flow cytometry analysis by meansof 7AAD staining.

FIG. 9 is a series of FCM pseudo-color plots showing sustainedexpression of NKG2D by anti-ILT5-exposed T cells despite persistentNKG2D engagement. 2×10⁵ CFSE-labeled PBMCs (responder population)/wellwere cultured with 2×10⁵ mitomycin-treated, allogeneic PBMCs (stimulatorpopulation) in the presence or absence of mIgG1 or TRX585 antibodies (50μg/ml). When indicated, blocking anti-NKG2D antibodies (clone 1D11 or5C6) were added to the cultures. In the latter blocking experiments,responder cells were incubated with 20 μg/ml of anti-NKG2D antibodiesfor 30 min at 37° C. prior to being mixed with stimulator cells.Anti-NKG2D antibodies were present at 10 μg/ml in the final cultures.After three and a half days, cells were stained with NKG2D, CD4 and CD8antibodies as well as 7AAD, and analyzed by flow cytometry.

FIG. 10 is a bar graph showing Fas ligand (FasL) secretion by T cellscontacted with APCs that have previously been contacted with TRX585antibodies. 2×10⁵ PBMCs (responder population)/well were cultured with2×10⁵ mitomycin-treated, allogeneic PBMCs (stimulator population) in thepresence or absence of TRX585 antibody (50 μg/ml). Fas ligand wasquantified in 24 hour culture supernatants using commercial human Fasligand-specific ELISA.

FIG. 11 is a series of line and bar graphs showing that T cells fromTRX585 antibody-containing PBMC cultures are cytotoxic to a variety ofhuman tumor cell lines. In the experiment shown in FIG. 11A, 4×10⁵CFSE-labeled PBMCs were cultured with mIgG1 or TRX585 antibody (50μg/ml). Three and a half days later, precultured T cells (effectorcells) were purified using a FACSAria™, based on CD4 and CD8 expression.On the same day, 50,000 CFSE-labeled U937 and KG1 tumor cells (targetcells) per well were mixed with effector cells at effector:target (E:T)ratios of 4:1, 1:1, 0.25:1 and 0:1 and cultured overnight. Cells weresubsequently stained with CD3, 7AAD and Annexin V, and occurrence ofapoptosis among target cells (CD3⁻CFSE⁺ cells) was examined by flowcytometry. The percentage of cytotoxicity was determined by summing thepercentage of late apoptotic (7AAD⁺ Annexin V⁺) and early apoptotic(7AAD⁻Annexin V⁺) cells. The left and right graphs show the percentagesof dead U937 and KG1 cells, respectively, when mixed with the indicatedproportion of either mIgG1 isotype control (black diamond) or TRX585(blue squares) antibody-precultured effector T cells. The X axesindicate effector:target ratios. The Y axes indicate percentcytotoxicity. In the experiment shown in FIG. 11B, effector T cells wereobtained and assessed for cytotoxic function against ARPE 19, U937, andHCT116 tumor cell lines (E:T=4:1) as described for FIG. 11A. The X axesindicate which tumor cell line was used. The Y axes indicate percentcytotoxicity. In the experiment shown in FIG. 11C, CD4 and CD8 T cellswere cell-sorted from 3.5 day-PBMC cultures, set up as described above,and assessed independently for cytotoxic function against ARPE 19, U937,HCT116 and K562 tumor cell lines (E:T=4:1). The X axes and the key tothe right of the graphs indicate which tumor cell line was used. The Yaxes indicate percent cytotoxicity.

FIG. 12A is a line graph showing that the cytotoxicity ofTRX585-preactivated T cells is MHC class I-dependent. FIG. 12B is a bargraph showing that the cytotoxicity of TRX585-preactivated T cells isFas ligand-dependent. Effector T cells were purified from mIgG1- orTRX585-containing PBMC cultures as well as cultures that did not containantibodies, and assessed for cytotoxicity against U937 tumor cellsaccording to the experimental procedure described for FIG. 11A. For MHCclass I blocking experiments, target cells were incubated withsaturating amounts of anti-pan human MHC class I antibody (20 μg/ml;clone W6/32) for 30 min and washed to remove unbound W6/32 antibodybefore exposure to T cells. To neutralize Fas ligand, 10 μg/ml ofblocking anti-human Fas ligand antibody (clone NOK-2) was added to thecocultures of effector and target cells. Data are representative ofseveral experiments using a variety of tumor cell lines and could berecapitulated when using either CD4 or CD8 effector T cells.

FIG. 13 is a series of FCM pseudo-color plots showing that, while CD4⁺and CD8⁺ T cells from PBMC cultures containing only TRX585 antibodiesdivided actively, concomitant treatment of PBMCs with anti-CD3 andTRX585 antibodies resulted in the inhibition of T cell proliferation.Here, 4×10⁵ CFSE-labeled PBMCs were cultured with the indicatedconcentration of either mIgG1 isotype control or TRX585 antibody, in thepresence or absence of soluble anti-CD3 antibody (10 μg/ml). Three andan half days later, dilution of the CFSE dye in CD4 and CD8 T cells wasexamined by flow cytometry. Numbers in plots indicate the proportion ofdividing cells. Dead cells were systematically excluded from the flowcytometry analysis by means of 7AAD staining.

FIG. 14 is a series of FCM pseudo-color plots (FIG. 14A) and line graphs(FIG. 14B) showing that pre-exposure of CD4⁺ and CD8⁺ T cells to TRX585antibodies increases their responsiveness to subsequent TCR stimulationas well as surface CD3 complexes. In the experiment shown in FIG. 14A,4×10⁵ CFSE-labeled PBMCs were cultured in the presence or absence ofmIgG1 isotype control or TRX585 antibody (50 μg/ml). After 3.5 days, theprecultured T cells as well as T cells from freshly isolated autologousPBMCs were cell-sorted using a FACSAria, CFSE-labeled and exposed toanti-CD3 antibody-mediated stimulation for another 2 days. The latterTCR stimulation used solid-phase anti-CD3 antibody at concentrations of0.03-10 μg/ml. CD4+ and CD8+ T cell proliferation was examined by flowcytometry as described previously. Numbers in plots indicate theproportion of dividing cells. Dead cells were systematically excludedfrom flow cytometry analyses by means of 7AAD staining. FIG. 14B showsthe amount of CD3 complexes at the surface of the same T cells,expressed as the mean fluorescence intensity of the cells when stainedwith a fluorescent anti-CD3 antibody.

DESCRIPTION OF CERTAIN EMBODIMENTS

Various aspects of the disclosure are described below.

Definitions

“Antibody” as the term is used herein refers to a protein that generallycomprises heavy chain polypeptides and light chain polypeptides. Antigenrecognition and binding occurs within the variable regions of the heavyand light chains. Single domain antibodies having one heavy chain andone light chain and heavy chain antibodies devoid of light chains arealso known. A given antibody comprises one of five types of heavychains, called alpha, delta, epsilon, gamma and mu, the categorizationof which is based on the amino acid sequence of the heavy chain constantregion. These different types of heavy chains give rise to five classesof antibodies, IgA (including IgA1 and IgA2), IgD, IgE, IgG (IgG1, IgG2,IgG3 and IgG4) and IgM, respectively. A given antibody also comprisesone of two types of light chains, called kappa or lambda, thecategorization of which is based on the amino acid sequence of the lightchain constant domains. IgG, IgD, and IgE antibodies generally containtwo identical heavy chains and two identical light chains and twoantigen combining domains, each composed of a heavy chain variableregion (V_(H)) and a light chain variable region (V_(L)). Generally IgAantibodies are composed of two monomers, each monomer composed of twoheavy chains and two light chains (as for IgG, IgD, and IgE antibodies);in this way the IgA molecule has four antigen binding domains, eachagain composed of a V_(H) and a V_(L). Certain IgA antibodies aremonomeric in that they are composed of two heavy chains and two lightchains. Secreted IgM antibodies are generally composed of five monomers,each monomer composed of two heavy chains and two light chains (as forIgG and IgE antibodies); in this way the IgM molecule has ten antigenbinding domains, each again composed of a V_(H) and a V_(L). A cellsurface form of IgM also exists and this has two heavy chain/two lightchain structure similar to IgG, IgD, and IgE antibodies.

“Chimeric antibody” as the term is used herein refers to an antibodythat has been engineered to comprise at least one human constant region.For example, one or all the variable regions of the light chain(s)and/or one or all the variable regions the heavy chain(s) of a mouseantibody (e.g., a mouse monoclonal antibody) may each be joined to ahuman constant region, such as, without limitation an IgG1 humanconstant region. Chimeric antibodies are typically less immunogenic tohumans, relative to non-chimeric antibodies, and thus offer therapeuticbenefits in certain situations. Those skilled in the art will be awareof chimeric antibodies, and will also be aware of suitable techniquesfor their generation. See, for example, Cabilly et al., U.S. Pat. No.4,816,567; Shoemaker et al., U.S. Pat. No. 4,978,775; Beavers et al.,U.S. Pat. No. 4,975,369; and Boss et al., U.S. Pat. No. 4,816,397, eachof which is incorporated herein by reference in its entirety.

“Complementarity determining region” or “CDR” as the terms are usedherein refer to short polypeptide sequences within the variable regionof both heavy and light chain polypeptides that are primarilyresponsible for mediating specific antigen recognition. CDRs have beendescribed by Kabat, et al., J. Biol. Chem. 252, 6609-6616 1977; byChothia, et al., J. Mol. Biol. 196:901-917, 1987; and by MacCallum, etal., J. Mol. Biol. 262:732-745, 1996, each of which is incorporatedherein by reference in its entirety. There are three CDRs (termed CDR1,CDR2, and CDR3) within each V_(L) and each V_(H).

“Fragment” or “antibody fragment” as the terms are used herein inreference to an antibody refer to a polypeptide derived from an antibodypolypeptide molecule (e.g., an antibody heavy or light chainpolypeptide) that does not comprise a full length antibody polypeptide,but which still comprises at least a portion of a full length antibodypolypeptide. Antibody fragments often comprise polypeptides thatcomprise a cleaved portion of a full length antibody polypeptide,although the term is not limited to such cleaved fragments. Since afragment, as the term is used herein in reference to an antibody,encompasses fragments that comprise single polypeptide chains derivedfrom antibody polypeptides (e.g. a heavy or light chain antibodypolypeptides), it will be understood that an antibody fragment may not,on its own, bind an antigen. For example, an antibody fragment maycomprise that portion of a heavy chain antibody polypeptide that wouldbe contained in a Fab fragment; such an antibody fragment typically willnot bind an antigen unless it associates with another antibody fragmentderived from a light chain antibody polypeptide (e.g., that portion of alight chain antibody polypeptide that would be contained in a Fabfragment), such that the antigen-binding site is reconstituted. Antibodyfragments can include, for example, polypeptides that would be containedin Fab fragments, F(ab′)₂ fragments, scFv (single chain Fv) fragments,diabodies, linear antibodies, multispecific antibody fragments such asbispecific, trispecific, and multispecific antibodies (e.g., diabodies,triabodies, tetrabodies), minibodies, chelating recombinant antibodies,tribodies or bibodies, intrabodies, nanobodies, small modularimmunopharmaceuticals (SMIP), binding-domain immunoglobulin fusionproteins, camelized antibodies, and V_(HH) containing antibodies. Itwill be appreciated that “antibody fragments” or “antibody polypeptidefragments” include “antigen-binding antibody fragments” and“antigen-binding antibody polypeptide fragments.” “Antigen-bindingantibody fragments” and “antigen-binding antibody polypeptide fragments”include, for example, “ILT5-binding antibody fragments” and“ILT5-binding antibody polypeptide fragments” and “ILT5-bindingfragments.”

“Framework region” as the term is used herein refers to amino acidsequences within the variable region of both heavy and light chainpolypeptides that are not CDR sequences, and are primarily responsiblefor maintaining correct positioning of the CDR sequences to permitantigen binding. Although the framework regions themselves typically donot directly participate in antigen binding, as is known in the art,certain residues within the framework regions of certain antibodies candirectly participate in antigen binding or can affect the ability of oneor more amino acids in CDRs to interact with antigen. Framework regionsare sometimes referred to as “FR.”

“Humanized antibody” as the term is used herein refers to an antibodythat has been engineered to comprise one or more human framework regionsin the variable region together with non-human (e.g., mouse, rat, orhamster) complementarity-determining regions (CDRs) of the heavy and/orlight chain. In certain embodiments, a humanized antibody comprisessequences that are entirely human except for the CDR regions. Humanizedantibodies are typically less immunogenic to humans, relative tonon-humanized antibodies, and thus offer therapeutic benefits in certainsituations. Those skilled in the art will be aware of humanizedantibodies, and will also be aware of suitable techniques for theirgeneration. See for example, Hwang, W. Y. K., et al., Methods 36:35,2005; Queen et al., Proc. Natl. Acad. Sci. USA, 86:10029-10033, 1989;Jones et al., Nature, 321:522-25, 1986; Riechmann et al., Nature,332:323-27, 1988; Verhoeyen et al., Science, 239:1534-36, 1988; Orlandiet al., Proc. Natl. Acad. Sci. USA, 86:3833-37, 1989; U.S. Pat. Nos.5,225,539; 5,530,101; 5,585,089; 5,693,761; 5,693,762; 6,180,370; andSelick et al., WO 90/07861, each of which is incorporated herein byreference in its entirety.

“Treg” or “regulatory T cell” as the terms are used herein refer to apopulation of T cells that function to suppress activation of the immunesystem and thereby maintain immune system homeostasis and tolerance toself-antigens. While a majority of regulatory T cells develops in thethymus, peripheral non-Treg cells can be instructed to commit into theregulatory T cell lineage as well. Regulatory T cells are enriched amongcells exhibiting a CD4⁺CD25^(hi) or a CD8⁺CD28⁻ phenotype, and manyexpress the forkhead family transcription factor (FOXP3). Regulatory Tcells are involved in modulating immune responses in mammalian subjectsafter their immune systems have successfully responded to foreignantigens, and are also involved in regulating immune responses that maypotentially attack the subjects' own tissues, thereby resulting inautoimmune diseases.

ILT5

Immunoglobulin-like transcripts (ILTs) are encoded by rapidly evolvinggenes found in human and non-human primates. Immunoglobulin-liketranscript 5 (“ILT5”) is a cell surface molecule that is a member of theimmunoglobulin superfamily that includes ILT1, ILT2, ILT3, IL4, ILT5,ILT6, ILT7 and ILT8 (Colonna et al., J. of Exp. Med., Volume 186, Number11, 1809-1818, 1997, incorporate herein by reference in its entirety).It has been established that the extracellular domain of ILT3, an ILTreceptor with inhibitory function, has the capacity to induce T cellhyporesponsiveness (see e.g., US Patent Application Publication No.2008/0038260, incorporated herein by reference in its entirety). Thisobservation suggests that upon interaction with ILT3, ILT3 ligandexpressed by T cells transduces an inhibitory signal.

ILT5 is also an inhibitory ILT receptor and is highly expressed onantigen-presenting cells (APCs), such as immature DCs and monocytes inhumans. Human ILT5 gene has been cloned and characterized (see e.g.,Colonna et al., J. of Exp. Med., Volume 186, Number 11, 1809-1818, 1997;Pfistershammer et al., Blood, September 10; 114(11):2323-32. Epub 2009Jul. 17; U.S. Pat. No. 6,448,035, each of which is incorporated hereinby reference in its entirety).

Effects of Anti-ILT5 Antibodies and ILT5-Binding Fragments Thereof onImmune Cells

Anti-ILT5 antibodies and ILT5-binding fragments thereof for use in thepresently disclosed methods induce T cell proliferation when theanti-ILT5 antibodies or ILT5-binding fragments are in monovalent form,but not when the anti-ILT5 antibodies or ILT5-binding fragments are inpolyvalent (crosslinked) form. As used in reference to anti-ILT5antibodies and ILT5-binding fragments described herein, “monovalent”refers to a single molecule of the anti-ILT5 antibody or ILT5-bindingfragment that is not crosslinked. For example a soluble anti-ILT5antibody comprising two antigen-binding sites is “monovalent” as theterm is used herein. Without wishing to be bound by theory, wehypothesize that upon interaction of ILT5 ligand-expressing T cells withILT5-expressing steady state APCs, engagement of the ILT5 ligand by ILT5induces inhibitory signals that increase the activation threshold of Tcells. Alternatively, ILT5:ILT5 ligand engagement may preclude theinteraction of ILT5 ligand with an undefined receptor of lower affinity,which would be immunostimulatory. By occupying, as well as inducing someinternalization of surface ILT5 molecules, monovalent anti-ILT5antibodies and ILT5-binding fragments for use in the presently disclosedmethods prevent the ILT5 ligand-ILT5 interaction, thereby eitherremoving inhibitory signals or allowing activating signals to takeplace, either of which would lower the activation threshold of T cells.The fact that monovalent anti-ILT5 antibodies (rather than antibodiesimmobilized on the plastic bottom of tissue culture wells) can bestimulatory (see Example 3) strongly indicates that ILT5 molecules,which comprise functional inhibitory motifs in their cytoplasmic domain,do not function as inhibitory receptors if not hypercrosslinked. WhenILT5 receptors are co-engaged by crosslinked anti-ILT5 antibodies orILT5-binding fragments (e.g., those bound to Fc receptors on APC or tothe bottom of plastic tissue culture wells), they become fullyinternalized, which precludes ILT5:ILT5 ligand interactions.Furthermore, crosslinked anti-ILT5 antibodies do not enhance T cellactivation. This suggests that crosslinked anti-ILT5 antibodies caninduce an inhibitory cascade in ILT5-expressing cells (e.g., APCs),which is strong enough to reprogram APCs such that these cells nowdisplay a function that counteracts the T cell-specific activationsignals (i.e. a tolerogenic function) that occur in the absence ofILT5:ILT5 ligand interactions. Thus, we hypothesize that as a result ofthe integration of activating and inhibitory signals (due to blockade ofILT5:ILT5 ligand interactions and ILT5 signaling into the APC,respectively), unchanged (opposing signals of similar strength) ordiminished immunity can be achieved.

As further described in more detail in the Examples section below,engagement of ILT5 on APCs with monovalent anti-ILT5 antibodies inautologous as well as allogeneic settings results in an upregulation ofNKG2D in näive T cells exposed to such APCs. NKG2D is an immune receptorwith an important role in tumor and viral immunity. Moreover, T cellsexposed to APCs that had previously been contacted with the anti-ILT5antibody maintain elevated levels of NKG2D under conditions thatnormally trigger its internalization. Such conditions typically includecontact of NKG2D with its ligand or with an agonist antibody or fragmentthat binds NKG2D. NKG2D internalization aids tumors and intracellularpathogens (e.g., viruses) in evading recognition by the immune system.Therefore, extending the time of NKG2D expression by appropriate cellsof the immune system (e.g., CD4+ and CD8+ T cells) can be advantageousin treating cancer and/or infections with intracellular pathogens. Inaddition, T cells that proliferate as a result of having interacted withAPCs that have been contacted with anti-ILT5 antibodies or ILT5-bindingfragments thereof significantly upregulate surface TCR:CD3 complexes andpresent with markedly increased responsiveness to subsequent TCRstimulation. Upon interaction with APCs that have been or are contactedwith the anti-ILT5 antibody, both CD4⁺ and CD8⁺ T cells secrete highlevels of Fas-ligand and subsequently exert potent, MHC class I- as wellas Fas-L-dependent, anti-tumor cytotoxic effects.

In certain embodiments, an anti-ILT5 antibody or an ILT5-bindingantibody fragment for use in the presently disclosed methods induces aresponse in a T cell, e.g., a CD4⁺ or CD8⁺ T cell, either in vivo or invitro, when contacted with an APC, which APC has been or is contactedwith the anti-ILT5 antibody or ILT5-binding fragment. In certainembodiments, such a response is a proliferative response and/or acytokine/chemokine producing response. In certain embodiments, a T cellresponse (e.g. a proliferative response) is proportional to the amountof anti-ILT5 antibody or ILT5-binding fragment contacted with the APC.In certain embodiments, a T cell response (e.g. a proliferativeresponse) is induced in a T cell that has not been exposed to an antigen(e.g., a näive T cell). In certain embodiments, the T cell response(e.g. a proliferative response) is induced in a memory T cell that haspreviously been exposed to an antigen. A T cell response induced by ananti-ILT5 antibody or an ILT5-binding antibody fragment for use in thepresently disclosed methods, e.g. a proliferative response, occurs inthe absence of TCR recognition of a MHC molecule. Thus, a T cellresponse mediated by such an anti-ILT5 antibody or ILT5-binding fragmentoccurs in a TCR-independent manner (e.g., the response does not requirerecognition of a MHC molecule by a TCR).

In certain embodiments, a T cell, e.g., a CD4⁺ or CD8⁺ T cell, either invivo or in vitro, upregulates expression of NKG2D on its surface whenthe T cell is contacted with an APC, which APC has been previouslycontacted with an anti-ILT5 antibody or an ILT5-binding antibodyfragment. As used in the present context, the term “upregulate” meansthat the T cell expresses a protein (e.g., NKG2D on the cell surface) ata higher level than a control T cell contacted with an APC that has notbeen contacted with the anti-ILT5 antibody or an ILT5-binding antibodyfragment. “Upregulates” refers to the condition of expressing more of agiven protein (e.g., NKG2D on the cell surface) when the control T cellexpresses some level of that protein. “Upregulates” also refers to thecondition of expressing any amount, e.g. any detectable amount, of agiven protein (e.g., NKG2D on the cell surface) when the control T celldoes not expresses that protein at all. In certain embodiments, a T cellmaintains expression of NKG2D on its surface under one or moreconditions in which the NKG2D is typically internalized from the cellsurface. Non-limiting examples of such conditions include engagement ofthe NKG2D with an NKG2D ligand expressed on the surface of a cell,engagement of the NKG2D with a secreted NKG2D ligand, and engagement ofthe NKG2D with an antibody or fragment that binds NKG2D.

In certain embodiments, a T cell, e.g., a CD4⁺ or CD8⁺ T cell, either invivo or in vitro, upregulates expression of a TCR and CD3 molecules(e.g., a TCR:CD3 complex) on its surface when the T cell is contactedwith an APC, which APC has been previously contacted with an anti-ILT5antibody or an ILT5-binding antibody fragment. In certain embodiments, aT cell secretes Fas ligand (FasL) at a higher level than a T cellcontacted with an APC that has not been contacted with the anti-ILT5antibody or the ILT5-binding fragment.

In certain embodiments, a T cell or its progeny, e.g., a CD4⁺ or CD8⁺ Tcell, either in vivo or in vitro, contacted with an APC, which APC hasbeen previously contacted with an anti-ILT5 antibody or an ILT5-bindingantibody fragment, exhibits cytotoxic potential. “Cytotoxic potential”as the term is used herein, refers to the state of being able to acquirecytotoxic activity when exposed to an antigen. Thus, in certainembodiments, a T cell or its progeny that exhibits cytotoxic potential(e.g., as a result if having been contacted with an APC that waspreviously contacted with an anti-ILT5 antibody or an ILT5-bindingantibody fragment) is induced to become cytotoxic when exposed to anantigen. A T cell exhibiting cytotoxic potential (e.g., a T cell or itsprogeny contacted with an APC, which APC has been previously contactedwith an anti-ILT5 antibody or an ILT5-binding antibody fragment) may beinduced to cytotoxicity upon exposure to any of a variety of antigens.For example, such a T cell may be exposed to a “cellular antigen”. Asused herein, the term “cellular antigen” refers to an antigen that canbe expressed on or in a cell of a subject. The “cellular antigen” can bean exogenous antigen, an endogenous antigen or both. As used herein, theterm “exogenous antigen” refers to an antigen that is administered to asubject. The term “exogenous antigen” includes foreign, non-endogenousantigens (see definition of “endogenous antigen” below), as well asantigens that are identical to antigens present in vivo in the body of asubject. As used herein, the term “endogenous antigen” refers to anantigen that is not administered to a subject, e.g., is present in thebody of the subject. In certain embodiments, a “cellular antigen” isreleased upon administration of a therapy (e.g., radiation or achemotherapeutic agent, as described more fully below). In certainembodiments, a “cellular antigen” comprises an antigen present on or ina tumor cell or an antigen-bearing APC. Alternatively, a “cellularantigen” can be cell-free, so long as it is capable of being expressedon or in a cell of a subject. In certain embodiments, the contact withantigen will generally have occurred at least one hour (e.g., at leasttwo hours, three hours, five hours, ten hours, 15 hours, 24 hours, twodays, fours days, one week, two weeks, or longer) after the contact withthe anti-ILT5 antibody or ILT5-binding fragment-contacted APC. Contactwith any of a variety of antigens will result in the transition fromhaving cytotoxic potential to cytotoxicity. In certain embodiments, a Tcell that exhibits cytotoxic potential may become cytotoxic when itbinds to or recognizes a cell that is cancerous, or a cell that isinfected with a bacterium, a virus, a fungus (including, e.g., a yeast),a protozoan, or a parasite. For example, a T cell that exhibitscytotoxic potential may become cytotoxic when it binds to a cell that isinfected with a bacterium, a virus, a fungus, a protozoan, or aparasite. Exemplary antigens of interest include those derived frominfectious agents and tumor antigens, wherein an immune responsedirected against the antigen serves to prevent or treat disease causedby the agent. Such antigens include, but are not limited to, proteins,glycoproteins, lipoproteins, glycolipids, and the like. Antigens ofinterest also include those which provide therapeutic benefit to asubject who is at risk of acquiring, or who is diagnosed as having, atumor. In certain embodiments, such antigens are administered to asubject who is at risk of acquiring, or who is diagnosed as having, atumor. Appropriate antigens include tumor vaccines, proteins, markersand the like that are associated with disease. In certain embodiments, atumor vaccine introduces a costimulatory protein with the aim ofbreaking the tolerogenic tumor environment.

Non-limiting examples of tumor antigens include, for example,tumor-associated glycoprotein TAG-72, HER-2, high M_(r) melanomaantigens that bind to the antibody 9.2.27, Lewis-Y-related carbohydrate(found on epithelial carcinomas), the IL-2 receptor p55 subunit(expressed on leukemia and lymphoma cells), the erbB2/p185carcinoma-related proto-oncogene (overexpressed in breast cancer),gangliosides (e.g., GM2, GD2, and GD3), epithelial tumor mucin (i.e.,MUC-1), carcinoembryonic antigen, ovarian carcinoma antigen MOv-18,squamous carcinoma antigen 17-1A, and malignant melanoma MAGE antigens(e.g., MAGE-1 and MAGE-3), and the like. Those skilled in the art willbe aware of other suitable tumor antigens that render cytotoxic T cellsor their progeny having cytotoxic potential as described herein.

Non-limiting examples of viral antigens include, but are not limited to,the nucleoprotein (NP) of influenza virus and the Gag proteins of HIV.Other antigens include, but are not limited to, HIV Env protein or itscomponent parts, gp120 and gp41, HIV Nef protein, and the HIV Polproteins, reverse transcriptase and protease. In addition, other viralantigens such as Ebola virus (EBOV) antigens, such as, for example, EBOVNP or glycoprotein (GP), either full-length or GP deleted in the mucinregion of the molecule (Yang Z-Y, et al. (2000) Nat Med 6:886-9, 2000),small pox antigens, hepatitis A, B or C virus, human rhinovirus such astype 2 or type 14, Herpes simplex virus, poliovirus type 2 or 3,foot-and-mouth disease virus (FMDV), rabies virus, rotavirus, influenzavirus, coxsackie virus, human papilloma virus (HPV), for example thetype 16 papilloma virus, the E7 protein thereof, and fragmentscontaining the E7 protein or its epitopes; and simian immunodeficiencyvirus (SIV) may be used. An antigen of interest need not be limited toantigens of viral origin. Parasitic antigens, such as, for example,malarial antigens are included, as are fungal antigens, bacterialantigens and tumor antigens. Non-limiting examples of bacterial antigensinclude: Bordetella pertussis (e.g., P69 protein and filamentoushaemagglutinin (FHA) antigens), Vibrio cholerae, Bacillus anthracis, E.coli antigens such as E. coli heat Labile toxin B subunit (LT-B), E.coli K88 antigens, and enterotoxigenic E. coli antigens, the Y.enterocolitica heat shock protein 60 (Mertz et al., J. Immunol.164(3):1529-1537, 2000) M. tuberculosis heat-shock proteins hsp60 andhsp70, Chlamydia trachomatis outer membrane protein (Ortiz et al.,Infect. Immun. 68(3):1719-1723, 2000), B. burgdorferi outer surfaceprotein (Chen et al., Arthritis Rheum. 42(9):1813-1823, 1999); L. majorGP63 (White et al., Vaccine 17(17):2150-2161, 1999 (and publishederratum in Vaccine 17(20-21):2755)), N. meningitidis meningococcalserotype 15 PorB protein (Delvig et al., Clin. Immunol. Immunopathol.85(2); 134-142, 1997), P. gingivalis 381 fimbrial protein (Ogawa, J.Med. Microbiol. 41(5):349-358, 1994), E. coli outer membrane protein F(Williams et al., Infect. Immun. 68(5):2535-2545, 2000). Other examplesof microbial antigens include Schistosoma mansoni P28 glutathioneS-transferase antigens (P28 antigens) and antigens of flukes,mycoplasma, roundworms, tapeworms, Chlamydia trachomatis, and malariaparasites, e.g., parasites of the genus plasmodium or babesia, forexample Plasmodium falciparum, and peptides encoding immunogenicepitopes from the aforementioned antigens. Each of the referencesdisclosed above is incorporated herein by reference in its entirety.

Any of a variety of anti-ILT5 antibodies or ILT5-binding antibodyfragments that mediate an indirect immunostimulatory effect and/orproliferative response on näive CD4⁺ or näive CD8⁺ T cells when such Tcells are contacted with an APC that has previously been contacted withthe anti-ILT5 antibody or ILT5-binding fragment (e.g., a monovalent formof the anti-ILT5 antibody or ILT5-binding fragment) can be used in thepresently disclosed methods. Moreover, any of a variety of anti-ILT5antibodies or ILT5-binding antibody fragments that results inupregulation of NKG2D or TCR:CD3 complexes in T cells (e.g., näive Tcells) exposed to such APCs can be used in the presently disclosedmethods. Moreover, any of a variety of anti-ILT5 antibodies orILT5-binding antibody fragments that endow a T cell or its progeny withcytotoxic potential when the T cell is contacted with an APC that haspreviously been contacted with the anti-ILT5 antibody or ILT5-bindingfragment (e.g., a monovalent form of the anti-ILT5 antibody orILT5-binding fragment) can be used in the presently disclosed methods.Those of ordinary skill in the art will be able to choose suitableanti-ILT5 antibodies or ILT5-binding fragments thereof for use in thepresently disclosed methods. For example, anti-IL5 antibodies andILT5-binding fragments that can be used in the presently disclosedmethods include, but are not limited to, the anti-IL5 antibodies andILT5-binding fragments described below, e.g., those comprising one ormore of SEQ ID NOs: 1-32.

Inhibition of T Cell Responses

In contrast to the immunoenhancing effects described above, APCs thathave been previously contacted with crosslinked anti-ILT5 antibodies maybe tolerogenic since T cells interacting with such APCs do not mount theT cell response that is observed when monovalent antibody is used. Thus,in certain embodiments, an anti-ILT5 antibody or ILT5-binding fragmentthereof for use in the presently disclosed methods might inhibit aresponse in a T cell, e.g., a CD4⁺ or CD8⁺ T cell, either in vivo or invitro, when contacted with an APC, which APC has been contacted with acrosslinked form of the ant-ILT5 antibody or ILT5-binding fragment, theT cell being contacted with antigen at the same time as or very close intime to the contact of the T cell with the APC previously contacted withthe anti-ILT5 antibody or ILT5-binding fragment. As used in reference toinhibition of T cell responses, “very close in time” means within atimeframe where the pharmacodynamic effects of the anti-ILT5 antibodieson the APCs are still exerted. Without wishing to be bound by anyparticular theory, it is hypothesized that factors such as, but notlimited to, the half-life of anti-ILT5 antibodies or ILT5-bindingfragments thereof will be important in determining what such timeframewill be. In certain embodiments, such a response is a proliferativeresponse. In certain embodiments, an inhibition of a T cell response(e.g. a proliferative response) is proportional to the amount ofcrosslinked anti-ILT5 antibody or ILT5-binding fragment contacted withthe APC. In certain embodiments, a T cell response (e.g. a proliferativeresponse) is inhibited when the anti-ILT5 antibody or ILT5-bindingfragment crosslinks or hypercrosslinks ILT5. As described herein, suchhypercrosslinking occurs when the ant-ILT5 antibody or ILT5-bindingfragment is in polyvalent form (e.g., bound to a solid support or to Fcreceptors (in vivo)), but not when the anti-ILT5 antibody orILT5-binding fragment is monovalent form.

In certain embodiments, an anti-ILT5 antibody or ILT5-binding antibodyfragment for use in the presently disclosed methods is used to inducetolerance in a subject (e.g., a human). For example, an anti-ILT5antibody or ILT5-binding antibody fragment can be administered to asubject at the same time as or very close in time to an antigen ofinterest.

Treatment of Diseases and Infections

Treatment Via Induction or Enhancement of a T Cell Response

Monovalent anti-ILT5 antibodies and ILT5-binding antibody fragments suchas those described in the section entitled “Effects of Anti-ILT5Antibodies and ILT5-Binding Fragments Thereof on Immune Cells”indirectly activate both CD4⁺ and CD8⁺ T cells in a TCR-independentmanner (e.g., activation does not require recognition of a MHC moleculeby a TCR), when such T cells are contacted with an APC that has been orstill is contacted with the anti-ILT5 antibody or ILT5-binding fragment.Such T cells or their progeny exhibit cytotoxic potential, whichcytotoxic potential can be exploited in the treatment of certainconditions by exposing the T cells or their progeny to an antigen, thusrendering the cells cytotoxic. Thus, such anti-ILT5 antibodies andILT5-binding fragments thereof may be used to treat any of a variety ofconditions in a subject (e.g., a human), including but not limited tocancers and infections.

In certain embodiments, anti-ILT5 antibodies and ILT5-binding fragmentsthereof for use in the presently disclosed methods may be used to treatany of a variety of cancers in a subject. Cancers are characterized byuncontrolled, abnormal growth of cells, and include all types ofhyperproliferative growth, hyperplastic growth, oncogenic processes,metastatic tissues or malignantly transformed cells, tissues, or organs,irrespective of histopathologic type or stage of invasiveness. Cancersthat can be treated include, but are not limited to, pancreatic cancer,melanomas, breast cancer, lung cancer, bronchus cancer, colorectalcancer, prostate cancer, pancreas cancer, stomach cancer, ovariancancer, urinary bladder cancer, peripheral nervous system cancer,esophageal cancer, cervical cancer, uterine or endometrial cancer,cancer of the oral cavity or pharynx, liver cancer, kidney cancer,testicular cancer, biliary tract cancer, small bowel or appendix cancer,salivary gland cancer, thyroid gland cancer, adrenal gland cancer,osteosarcoma, chondrosarcoma, and cancers of hematological tissues.

In certain embodiments, an anti-ILT5 antibody or an ILT5-bindingfragment thereof is used in combination with another therapy to treatcancer. For example, an anti-ILT5 antibody or ILT5-binding fragmentthereof may be used in combination with radiation therapy. Additionallyor alternatively, an anti-ILT5 antibody or ILT5-binding fragment may beused in combination with a chemotherapeutic agent. In certainembodiments, the therapy is administered, at least once, at the sametime as or very close in time to administration of the anti-ILT5antibody or the ILT5-binding fragment. As used in reference to a therapyadministered in combination with an anti-ILT5 antibody or ILT5-bindingfragment, “very close in time” means within a timeframe within which Tcells display pharmacodynamic effects due to the anti-ILT5 antibodies orILT5-binding fragments.

The timing of therapy administration relative to that of the anti-ILT5antibody or ILT5-binding fragment administration will take into accountseveral parameters: On one hand, factors that are known to influence thein vivo kinetics of antigen-specific T cell activation and responses,which are initiated in secondary lymphoid tissues (e.g. lymph nodes)through contacts between T cells and antigen-bearing DCs, will beconsidered. For instance, the abundance, immunogenicity and availabilityof an antigen are obviously important and dictate whether T cellresponses will be initiated, as well as their overall strength andduration. The affinity of a single TCR for a peptide:MHC complex isanother parameter. In this regard and without wishing to be bound by anyparticular theory, we hypothesize that by increasing TCR:CD3 complexeson the surface of T cells, anti-ILT5 antibodies or ILT5-bindingfragments thereof increase the avidity of T cells for antigen-bearingDCs and thereby not only permit the recruitment of T cells with lowaffinity TCRs into a response in which these T cells would otherwise nothave participated but also accelerate the overall kinetics of T cellactivation. The kinetics of T cell activation also depend on whether DCsacquire the antigen of interest within or outside the lymph nodes (e.g.,in the blood stream or a peripheral non-lymphoid tissue). In the lattercase, the time required for antigen-bearing DCs to traffic to the lymphnodes increases the timing within which T cell activation occursrelative to the time of antigen exposure. On the other hand, in vitrodata show that concomitant TCR stimulation and exposure of CD4⁺ and CD8⁺T cells to anti-ILT5 antibody abrogates anti-ILT5 antibody-induced Tcell responsiveness (see FIG. 13). Thus and without wishing to be boundby any particular theory, it is hypothesized that it is desirable toallow the anti-ILT5 antibodies or ILT5-binding fragments to exert theirpharmacodynamic effects on T cells prior to the initiation ofantigen-specific T cell activation, which activation is induced throughantigen exposure by means of therapy administration. In addition, is itdesirable to administer the anti-ILT5 antibody or ILT5-binding fragmentcloser in time to the antigen of interest when the anti-ILT5 antibody orILT5-binding fragment has a relatively short half-life. Determining thehalf-life of administered antibodies or antigen-binding fragments isroutine in the art, and can be accomplished by a variety of methodsincluding, but not limited to, measuring the amount of antibody orfragment in serum levels (e.g., by ELISA) at various times postadministration and fitting such measurements to a half-life curve. Otherfactors that can influence the length of time between administrationsinclude, without limitation, a patient's physiological reaction or lackthereof to the anti-ILT5 antibody or ILT5-binding fragment, the natureof the therapy and practical considerations such as minimizing thenumber of clinic visits. Those skilled in the art are aware of the abovefactors and will be able to determine which timing of therapyadministration is appropriate. In certain embodiments a therapy (e.g.radiation or a chemotherapeutic agent) is administered subsequent toadministration of the anti-ILT5 antibody or ILT5-binding fragment. Forexample, a therapy can be administered several hours or days after theanti-ILT5 antibody or ILT5-binding fragment. In other embodiments, atherapy (e.g. radiation or a chemotherapeutic agent) is administeredprior to or concomitantly with administration of the anti-ILT5 antibodyor ILT5-binding fragment. For example, a therapy can be administered atthe same time as, or several hours or days prior to the anti-ILT5antibody or ILT5-binding fragment.

In certain embodiments, the therapy consists of a bonemarrow/hematopoietic cell transplant (BMT/HCT) in a subject with ahematopoietic tumor. In such embodiments, anti-ILT5 antibodies orILT5-binding fragments thereof may be administered in a subject showingsigns of tumor recurrence, thus after to the therapy (BMT/HCT). In thelatter case and without wishing to be bound by theory, it ishypothesized that anti-ILT5 antibodies or ILT5-binding fragments thereofwill induce and/or enhance T cell responses including those targetingtumor cells. In such embodiments, anti-ILT5 antibodies or ILT5-bindingfragments thereof are administered anytime after tumor relapse isdiagnosed.

In certain embodiments, administration of a therapy (e.g., radiation ora chemotherapeutic agent) inhibits or prevents the function of cellsand/or causes destruction of cells, e.g., acts to lyse or otherwisedisrupt (e.g., by inducing apoptosis) cells that comprise an antigen ofinterest, thereby providing a source of antigen that will activate thecytotoxic potential of a T cell or its progeny that has interacted withan APC contacted with an anti-ILT5 antibody or an ILT5-binding fragmentthereof. In certain embodiments, a therapy releases a cellular antigenfrom a cell (e.g., a tumor cell or a cell infected with a virus),thereby providing a source of antigen that will activate the cytotoxicpotential of a T cell that has interacted with an APC contacted with ananti-ILT5 antibody or an ILT5-binding fragment thereof. In certainembodiments, a therapy (e.g. a tumor vaccine) introduces a substantialamount of a tumor antigen, wherein the antigen does not inducesufficient immunity to eradicate tumor cells when expressed endogenouslyin the tumor environment. In certain embodiments, the tumor vaccine canalso introduce costimulatory molecules. When the therapy is administeredprior to the antibody or ILT5-binding fragment, it will be understoodthat the kinetics of the antigen-mediated T cell response may be slowerthan the kinetics of anti-ILT5 antibody-mediated T cell responses, asdescribed below, and thus cytotoxicity of the T cell towards such anantigen is induced or enhanced. In certain embodiments, anti-ILT5antibodies and ILT5-binding antibody fragments thereof may be used totreat a subject suffering from a tumor. In certain embodiments, a tumoris poorly immunogenic or even tolerogenic. In such embodiments, anantigen of interest that may potentially trigger cytotoxicity of a Tcell as described herein may also be poorly immunogenic or eventolerogenic, e.g., as a result of being in a tumor environment. Incertain embodiments, administration of a therapy (e.g., achemotherapeutic agent or radiation therapy) as described above releasesone or more antigens from the tumor in a manner such that the antigen isno longer poorly immunogenic or tolerogenic. As a result, APCs that havepreviously been bound by and anti-ILT5 antibodies or an ILT5-bindingantibody fragment may bind T cells, which T cells can be induced tobecome cytotoxic upon binding or recognizing an antigen released by thetherapy. In certain embodiments, a tumor cell expresses ILT5 receptors,which bind to ILT5 ligands on a T cell that recognizes an antigen on thetumor cell. In such embodiments, ILT5:ILT5 ligand interactions prohibitthe activation of the T cell that is bound to the tumor cell. Thus incertain embodiments, administration of anti-ILT5 antibodies orILT5-binding fragments thereof, with or without therapy, preventsILT5:ILT5 ligand interactions between the T cell and the tumor cell,which permits the activation of the T cell that is bound to the tumorcell.

In certain embodiments, a therapy is administered until a desiredendpoint is reached. For example, a therapy may be administered until adesired level of inhibition of tumor growth, reduction in tumor size,reduction in the number of tumors, decrease in tumor burden, and/orprolonging of survival time is reached. Those skilled in the art will beaware of these and other desired endpoints, and will be able todetermine when such an endpoint is reached using standard methods.

A variety of radiation therapies are known in the art, including forexample, external beam radiotherapy (EBRT or XBRT) or teletherapy whichis applied from outside the body, brachytherapy or sealed sourceradiotherapy in which sealed radioactive sources are placed in the areaunder treatment, and systemic radioisotope therapy or unsealed sourceradiotherapy which is administered by infusion or oral ingestion. Avariety of external beam radiotherapies are known, including but notlimited to, conventional 2D external beam radiotherapy (2DXRT),stereotactic radiation, 3-dimensional conformal radiotherapy (3DCRT),and intensity-modulated radiation therapy (IMRT). Brachytherapy canemploy temporary or permanent placement of radioactive sources. Thoseskilled in the art will be aware of these and other radiation therapiesand will be able to appropriately administer them.

A variety of chemotherapeutic agents are known in the art. In certainembodiments, a chemotherapeutic agent used in combination with ananti-ILT5 antibody or ILT5-binding antibody fragment is anantimetabolite. Non-limiting examples of anti-metabolites includeAminopterin, Methotrexate, Pemetrexed, Raltitrexed, Cladribine,Clofarabine, Fludarabine, Mercaptopurine, Pentostatin, Thioguanine,Capecitabine, Cytarabine, Fluorouracil, Floxuridine, and Gemcitabine. Incertain embodiments, an antimetabolite is a nucleoside analogue such as,without limitation, gemcitabine or fluorouracil. In certain embodiments,a chemotherapeutic agent used in combination with an anti-ILT5 antibodyor an ILT5-binding fragment thereof is an agent that affects microtubuleformation. Non-limiting examples of agents that affects microtubuleformation include paclitaxel, docetaxel, vincristine, vinblastine,vindesine, vinorelbin, taxotere, etoposide, and teniposide. In certainembodiments, the chemotherapeutic agent used in combination with ananti-ILT5 antibody or an ILT5-binding fragment thereof is an alkylatingagent such as, e.g., cyclophosphamide. In certain embodiments, achemotherapeutic agent used in combination with an anti-ILT5 antibody oran ILT5-binding fragment thereof is a cytotoxic antibiotic, e.g., atopoisomerase II inhibitor such as doxorubicin. In certain embodiments,a chemotherapeutic agent comprises a toxin such as a small-moleculetoxin or an enzymatically active toxin of bacterial, fungal, plant, oranimal origin, or fragments thereof. In certain embodiments. achemotherapeutic agent used in combination with an anti-ILT5 antibody orILT5-binding fragment is an anti-angiogenic agent such as e.g. avastin.In certain embodiments. a chemotherapeutic agent used in combinationwith an anti-ILT5 antibody or ILT5-binding fragment thereof is abiologic agent such as e.g. herceptin.

In certain embodiments, anti-ILT5 antibodies and ILT5-binding fragmentsthereof for use in the presently disclosed methods may be used to treator prevent (e.g. in combination with vaccination) any of a variety ofinfections in a subject. Exemplary infections include any of a varietyof bacterial (e.g., an intracellular bacterium), viral, fungal,protozoan, or parasitic (e.g., an intracellular parasitic) infections.Viral infections that can be treated include, but are not limited to,infections caused by HIV (e.g., HIV-1 and HIV-2), human herpes viruses,cytomegalovirus (esp. human), rotavirus, epstein-barr virus, varicellazoster virus, hepatitis viruses, such as hepatitis B virus, hepatitis Avirus, hepatitis C virus and hepatitis E virus, paramyxoviruses:respiratory syncytial virus, parainfluenza virus, measles virus, mumpsvirus, human papilloma viruses (for example HPV6, 11, 16, 18 and thelike), flaviviruses (e.g. yellow fever virus, dengue virus, tick-borneencephalitis virus, Japanese encephalitis virus), and influenza virus.

Bacterial infections include, but are not limited to, infections causedby Neisseria spp, including N. gonorrhea and N. meningitidis,Streptococcus spp, including S. pneumoniae, S. pyogenes, S. agalactiae,S. mutans; Haemophilus spp, including H. influenzae type B, non typeableH. influenzae, H. ducreyi; Moraxella spp, including M. catarrhalis, alsoknown as Branhamella catarrhalis; Bordetella spp, including B.pertussis, B. parapertussis and B. bronchiseptica; Mycobacterium spp.,including M. tuberculosis, M. bovis, M. leprae, M. avium, M.paratuberculosis, M. smegmatis; Legionella spp, including L.pneumophila; Escherichia spp, including enterotoxic E. coli,enterohemorragic E. coli, enteropathogenic E. coli; Vibrio spp,including V. cholera, Shigella spp, including S. sonnei, S. dysenteriae,S. flexnerii; Yersinia spp, including Y. enterocolitica, Y. pestis, Y.pseudotuberculosis, Campylobacter spp, including C. jejuni and C. coli;Salmonella spp, including S. typhi, S. paratyphi, S. choleraesuis, S.enteritidis; Listeria spp., including L. monocytogenes; Helicobacterspp, including Hpylori; Pseudomonas spp, including P. aeruginosa,Staphylococcus spp., including S. aureus, S. epidermidis; Enterococcusspp., including E. faecalis, E. faecium; Clostridium spp., including C.tetani, C. botulinum, C. difficile; Bacillus spp., including B.anthracis; Corynebacterium spp., including C. diphtheriae; Borreliaspp., including B. burgdorferi, B. garinii, B. afzelii, B. andersonii,B. hermsii; Ehrlichia spp., including E. equi and the agent of the HumanGranulocytic Ehrlichiosis; Rickettsia spp, including R. rickettsii;Chlamydia spp., including C. trachomatis, C. neumoniae, C. psittaci;Leptsira spp., including L. interrogans; Treponema spp., including T.pallidum, T. denticola, and T. hyodysenteriae.

In certain embodiments, an anti-ILT5 antibody or an ILT5-bindingfragment thereof for use in the presently disclosed methods can be usedto induce and/or enhance an immune response in a subject. In suchembodiments, the anti-ILT5 antibody or ILT5-binding fragment acts as anadjuvant by inducing or enhancing an immune response (e.g., a cytotoxiccell immune response) against an antigen of interest. For example, asubject may first be administered an anti-ILT5 antibody or anILT5-binding fragment thereof without concomitant administration of anantigen of interest. Without wishing to be bound by theory, it ishypothesized that such administration endows certain näive T cells inthe subject with cytotoxic potential. Subsequently, a subject may beadministered an antigen of interest. Again without wishing to be boundby theory, it is hypothesized that certain T cells exhibiting cytotoxicpotential are rendered cytotoxic to cells expressing that antigen ofinterest upon exposure to the antigen. Thus, in certain embodiments,cytotoxicity of at least one T cell in the subject towards a cell thatcomprises the antigen is induced or enhanced. In certain embodiments,one or more additional antigens are provided by direct administration ofthe antigen to the subject. In certain embodiments, an antigen providedby direct administration is the same antigen as is released from a lysedor disrupted cell upon administration of a therapy.

As discussed previously, a suitable length of time betweenadministration of the anti-ILT5 antibody or ILT5-binding fragment andthe antigen of interest will depend on various factors, each of whichcan be determined by those skilled in the art. In certain embodiments,the anti-ILT5 antibody or ILT5-binding fragment can be administered 1-14days (e.g., 3 days) before administration of the antigen of interest. Incertain embodiments, an antigen is administered prior to orconcomitantly with administration of the anti-ILT5 antibody orILT5-binding fragment. For example, a therapy can be administered as thesame time as, or several hours or days prior to the anti-ILT5 antibodyor ILT5-binding fragment.

In certain embodiments, a subject may be administered an anti-ILT5antibody or an ILT5-binding antibody fragment at or about the same timeas an antigen of interest to induce or enhance an immune response in asubject. As described in more detail herein, a proliferative T cellresponse is induced in vitro in allogeneic mixed lymphocyte culturesthat simultaneously contain both an anti-ILT5 antibody and a foreignantigen present on a foreign lymphocyte. In contrast, anti-ILT5antibody-induced proliferation of a T cell simultaneously exposed ananti-CD3 antibody-mediated stimulation and an APC that has been affectedby an anti-ILT5 antibody is inhibited. Without wishing to be bound bytheory, it is possible to reconcile these results by the differentialkinetics of the antigen-mediated and anti-ILT5 antibody-mediated T cellresponses. T cell proliferation in allogeneic mixed lymphocyte reactionstypically occurs at day 5-9 due to the fact that it takes some time forthe T cells to establish stable contacts with APCs, which is anessential component of the T cell activation process. In contrast,anti-ILT5 mediated T cell proliferation is detected as soon as 24 hours,and peaks at day 3-3.5, similar to stimulation of T cell proliferationobserved with anti-CD3 antibodies. Thus, the kinetics of theantigen-mediated T cell responses are slower than the kinetics ofanti-ILT5 antibody-mediated T cell responses. Another possibility, againwithout wishing to be bound by theory, is that one or more ILT5 ligandsand TCR complexes in the mixed lymphocyte culture compete for a moleculethat is involved in the observed T cell proliferation.

In certain embodiments, the subject is also administered an adjuvant(e.g., administered with the antigen of interest) to bolster thesubject's immune response against the antigen. Suitable adjuvantsinclude, without limitation, CpG, alum, oil-in-water emulsions (e.g.,MF59™ (a sub-micron oil-in-water emulsion of a squalene, polyoxyethylenesorbitan monooleate, and sorbitan trioleate), Montanide (Seppic),Adjuvant 65, Lipovant), immune stimulating complexes or ISCOMs(honeycomb-like structures composed of typically Quillaja saponins,cholesterol, and phospholipids), QS-21 (a natural product of the bark ofthe Quillaja saponaria tree species), and inulin-based adjuvants.

In certain embodiments, an anti-ILT5 antibody or ILT5-binding antibodyfragment is used to induce or enhance an immunostimulatory response in aT cell in vitro, which T cell is then administered to a subject, eitheralone or in combination with one or more therapeutic agents. Forexample, PBMCs from a given subject can be cultured with an anti-ILT5antibody or an ILT5-binding fragment thereof. In these cultures, T cells(e.g., a CD4⁺ or CD8⁺ T cell) will interact with APCs that have beencontacted with an anti-ILT5 antibody or ILT5-binding fragment thereofand they or their progeny will acquire a cytotoxic potential. The T cellcan then be contacted with an antigen of interest, rendering the T cellcytotoxic to cells having the antigen of interest on their surface. Thiscontacting with antigen can be in vitro prior to the administration ofthe cells to the subject or it can be in vivo after the administrationof the cells to the subject. The cytotoxicity of T cells generated bysuch methods can be evaluated by those skilled in the art according toroutine methods. T cells that exhibit suitable cytotoxicity can be beinfused in the subject they came from to treat a disease or conditionassociated with the antigen of interest. Alternatively, a T cell havingcytotoxic potential as a result of having been contacted with an APCpreviously contacted with an anti-ILT5 antibody or ILT5-binding fragmentthereof described herein in an autologous setting, or its progeny havingsuch cytotoxic potential, may be infused in the subject it came from,wherein the T cell become cytotoxic upon exposure to an antigen in vivo.In certain embodiments, only CD4⁺ T cells are made cytotoxic and infusedin a subject. In certain embodiments, only CD8⁺ T cells are madecytotoxic and infused in a subject. In certain embodiments, a populationof T cells comprising both CD4⁺ and CD8⁺ T cells is made cytotoxic andinfused in a subject.

In certain embodiments, a cell is obtained from a subject and a nucleicacid molecule encoding an anti-ILT5 antibody or ILT5-binding antibodyfragment is introduced into the cell. For example, the nucleic acidmolecule may be operatively linked to a promoter or other sequence thatmediates expression of the anti-ILT5 antibody or the ILT5-bindingfragment in that cell. In certain embodiments, the nucleic acid moleculemay also comprise one or more sequences encoding a polypeptide moietythat mediates secretion, which sequences are operatively linked (e.g.,in frame) to the sequences encoding the ant-ILT5 antibody or theILT5-binding fragment, such that the anti-ILT5 antibody or ILT5-bindingfragment is secreted from the cell. Such cells obtained from a subjectand containing the introduced nucleic acid molecule, or the progeny ofsuch cells, can then be introduced back into the subject, such that thecell secretes the anti-ILT5 antibody or ILT5-binding antibody fragmentin vivo. Naturally, where the progeny of the cells obtained from thesubject are used, they also should contain and express the nucleic acidmolecule. The cells to be administered back to the subject canoptionally be treated so as to prevent or inhibit their proliferationafter administration. They can be treated with, for example, anappropriate dose of ionizing radiation (e.g., x- or gamma-irradiation)or a drug such as mitomycin-C.

As will be appreciated by those skilled in the art upon reading thepresent disclosure, an anti-ILT5 antibody or ILT5-binding antibodyfragment produced by cells as described above (e.g., produced by ex vivomethods) will be useful in inducing T cell proliferation, and ininducing T cells to exhibit cytotoxic potential and/or cytotoxicity.

Treatment Via Inhibition of a T Cell Response

In certain embodiments, an anti-ILT5 antibody or an ILT5-bindingantibody fragment for use in the presently disclosed methods is used toinduce tolerance as described above in order to treat an immune-relateddisease. “Immune-related disease” as the term is used herein refers to adisease that is associated with at least one abnormal immune phenomenon.For example, one class of immune-related diseases comprises autoimmunediseases. An autoimmune disease typically results when the subject'simmune system is activated against one or more components (cells,tissues, or cell/tissue-free molecules) of the subject and attacks thatsubject's own organs, tissues or cells, instead of attacking, forexample, foreign bacteria, viruses and other infectious agents or cancercells. Every mammalian subject exhibits autoimmunity to some extent, butsuch autoimmunity normally does not result in a disease state since theimmune system regulates and suppresses normal autoimmunity. Autoimmunediseases develop when there is a disruption in the immune system'sregulation. Autoimmune diseases can also result when there is amolecular alteration in a subject's cell that is recognized by theimmune system, such that the immune system recognizes the altered cellas “foreign.”

Another example of an immune-related disease is a disease associatedwith the effects of organ, tissue, or cell transplantation. Transplantedcells rarely exhibit that same antigens on their surfaces as therecipient subject's endogenous cells. Thus, a transplant subject'simmune system often attacks and rejects transplanted solid tissues,which can lead to organ failure or other serious systemic complications.Certain immunosuppressive drugs are typically used to mediate or preventthese immune attacks, but such drugs often cause undesirable sideeffects, including for example, the risk of developing opportunisticinfections as a result of decreased immune responses. Exemplaryimmune-related diseases include, but are not limited to, adrenergic drugresistance, alopecia greata, ankylosing spondylitis, antiphospholipidsyndrome, autoimmune Addison's disease, autoimmune diseases of theadrenal gland, allergic encephalomyelitis, autoimmune hemolytic anemia,autoimmune hepatitis, autoimmune inflammatory eye disease, autoimmuneneonatal thrombocytopenia, autoimmune neutropenia, autoimmune oophoritisand orchitis, autoimmune thrombocytopenia, autoimmune thyroiditis,Behcet's disease, bullous pemphigoid, cardiomyopathy, cardiotomysyndrome, celiac sprue-dermatitis, chronic active hepatitis, chronicfatigue immune dysfunction syndrome (CFIDS), chronic inflammatorydemyelinating polyneuropathy, Churg-Strauss syndrome, cicatricalpemphigoid, CREST syndrome, cold agglutinin disease, Crohn's disease,dense deposit disease, diseases associated with effects from organtransplantation, discoid lupus, essential mixed cryoglobulinemia,fibromyalgia-fibromyositis, glomerulonephritis (e.g., IgA nephrophathy),gluten-sensitive enteropathy, Goodpasture's syndrome, GVHD, Graves'disease (including e.g., Graves thyroiditis and Graves ophthalmopathy),Guillain-Barre, hyperthyroidism (i.e., Hashimoto's thyroiditis),idiopathic pulmonary fibrosis, idiopathic Addison's disease, idiopathicthrombocytopenia purpura (ITP), IgA neuropathy, Insulin ResistanceSyndrome, juvenile arthritis, lichen planus, lupus erythematosus,Meniere's disease, Metabolic Syndrome, mixed connective tissue disease,multiple sclerosis, Myasthenia Gravis, myocarditis, diabetes (e.g., TypeI diabetes or Type II diabetes), neuritis, other endocrine glandfailure, pemphigus vulgaris, pernicious anemia, polyarteritis nodosa,polychrondritis, Polyendocrinopathies, polyglandular syndromes,polymyalgia rheumatica, polymyositis and dermatomyositis, post-MI,primary agammaglobulinemia, primary biliary cirrhosis, psoriasis,psoriatic arthritis, Raynauld's phenomenon, relapsing polychondritis,Reiter's syndrome, rheumatic heart disease, rheumatoid arthritis,sarcoidosis, scleroderma, Sjogren's syndrome, stiff-man syndrome,systemic lupus erythematosus, takayasu arteritis, temporalarteritis/giant cell arteritis, ulcerative colitis, urticaria, uveitis,Uveitis Ophthalmia, vasculitides such as dermatitis herpetiformisvasculitis, vitiligo, and Wegener's granulomatosis.

In certain embodiments, a crosslinked anti-ILT5 antibody or anILT5-binding antibody fragment is administered in combination withanother therapeutic agent that induced tolerance. A non-limiting exampleof such a tolerance-inducing therapeutic agent is an antibody orantigen-binding fragment thereof that binds CD3, e.g., otelixizumab(Keymeulen B, et al. N Engl J. Med.; 352:2598-2608, 2005 incorporatedherein by reference in its entirety. Other anti-CD3 antibodies include,without limitation, hOKT3 (humanized (IgG1 or IgG4) anti-human CD3),HUM291 (humanized (IgG2) anti-human CD3; visilizumab; NUVION™), UCHT1(mouse (IgG1) anti-human CD3), Leu4 (mouse (IgG1) anti-human CD3), 500A2(hamster (IgG) anti-mouse CD3), CLB-T3/3 (mouse (IgG2a) anti-human CD3),BMA030 (mouse (IgG2a) anti-human CD3), YTH 12.5 (rat (IgG2b) anti-humanCD3), and NI-0401 (fully human anti-human CD3). Those skilled in the artwill be aware of other anti-CD3 antibodies and fragments that can beused in combination with anti-ILT5 antibodies and ILT5-binding fragmentsthereof disclosed herein.

In certain embodiments, an anti-ILT5 antibody or an ILT5-bindingantibody fragment that is administered to a subject is crosslinked orotherwise aggregated. As indicated above, without wishing to be bound byany particular theory, it is hypothesized that co-engagement of ILT5receptors by crosslinked anti-ILT5 antibodies and ILT5-binding fragmentsdescribed herein, initiates an inhibitory cascade in ILT5-expressingAPCs, which renders them tolerogenic.

Treatment Generally

In certain embodiments, an anti-ILT5 antibody or ILT5-binding antibodyfragment is administered to a subject directly. Routes of administrationare described in more detail in the section entitled “PharmaceuticalCompositions.” A therapeutically active amount of an anti-ILT5 antibodyor ILT5-binding fragment can be administered in an amount effective, atdosages and for periods of time necessary to achieve the desired result.For example, a therapeutically active amount of anti-ILT5 antibody orILT5-binding fragment thereof may vary according to factors such as thedisease state, age, sex, and weight of the subject, and the ability ofthe anti-ILT5 antibody or ILT5-binding fragment to elicit a desiredresponse in the subject. Dosage regimens can be adjusted to provide theoptimum therapeutic response. For example, several divided doses can beadministered daily or the dose can be proportionally reduced asindicated by the exigencies of the therapeutic situation. Those skilledin the art will be aware of dosages and dosing regimens suitable foradministration of an anti-ILT5 antibody or ILT5-binding fragment to asubject. See e.g., Physicians' Desk Reference, 63rd edition, ThomsonReuters, Nov. 30, 2008, incorporated herein by reference in itsentirety.

Those skilled in the art will be aware of other diseases and conditionsthat can be treated using any of a variety of anti-ILT5 antibodies andILT5-binding fragments.

Pharmaceutical Formulations

Anti-ILT5 antibodies or ILT5-binding antibody fragments described hereinmay be formulated for delivery by any available route including, but notlimited to parenteral (e.g., intravenous), intradermal, subcutaneous,oral, nasal, bronchial, ophthalmic, transdermal (topical), transmucosal,rectal, and vaginal routes. Anti-ILT5 antibodies or ILT5-bindingfragments thereof may include a delivery agent (e.g., a cationicpolymer, peptide molecular transporter, surfactant, etc., as describedabove) in combination with a pharmaceutically acceptable carrier. Asused herein the term “pharmaceutically acceptable carrier” includessolvents, dispersion media, coatings, antibacterial and antifugalagents, isotonic and absorption delaying agents, and the like,compatible with pharmaceutical administration. Supplementary activecompounds can also be incorporated into pharmaceutical formulationscomprising an anti-ILT5 antibody or an ILT5-binding fragment thereof asdescribed herein.

A pharmaceutical composition is formulated to be compatible with itsintended route of administration. Solutions or suspensions used forparenteral, intradermal, or subcutaneous application can include thefollowing components: a sterile diluent such as water for injection,saline solution, fixed oils, polyethylene glycols, glycerine, propyleneglycol or other synthetic solvents; antibacterial agents such as benzylalcohol or methyl parabens; antioxidants such as ascorbic acid or sodiumbisulfite; chelating agents such as ethylenediaminetetraacetic acid;buffers such as acetates, citrates or phosphates and agents for theadjustment of tonicity such as sodium chloride or dextrose. pH can beadjusted with acids or bases, such as hydrochloric acid or sodiumhydroxide. The parenteral preparation can be enclosed in ampoules,disposable syringes or multiple dose vials made of glass or plastic.

Pharmaceutical compositions suitable for injectable use typicallyinclude sterile aqueous solutions (where water soluble) or dispersionsand sterile powders for the extemporaneous preparation of sterileinjectable solutions or dispersion. For intravenous administration,suitable carriers include physiological saline, bacteriostatic water,Cremophor EL™ (BASF, Parsippany, N.J.) or phosphate buffered saline(PBS). In all cases, the composition should be sterile and should befluid to the extent that easy syringability exists. Pharmaceuticalformulations are ideally stable under the conditions of manufacture andstorage and should be preserved against the contaminating action ofmicroorganisms such as bacteria and fungi. In general, the relevantcarrier can be a solvent or dispersion medium containing, for example,water, ethanol, polyol (for example, glycerol, propylene glycol, andliquid polyetheylene glycol, and the like), and suitable mixturesthereof. The proper fluidity can be maintained, for example, by the useof a coating such as lecithin, by the maintenance of the requiredparticle size in the case of dispersion and by the use of surfactants.Prevention of the action of microorganisms can be achieved by variousantibacterial and antifungal agents, for example, parabens,chlorobutanol, phenol, ascorbic acid, thimerosal, and the like. In manycases, it will be advantageous to include isotonic agents, for example,sugars, polyalcohols such as manitol, sorbitol, or sodium chloride inthe composition. Prolonged absorption of the injectable compositions canbe brought about by including in the composition an agent which delaysabsorption, for example, aluminum monostearate and gelatin.

Sterile injectable solutions can be prepared by incorporating theanti-ILT5 antibody or ILT5-binding fragment in the required amount in anappropriate solvent with one or a combination of ingredients enumeratedabove, as required, followed by filtered sterilization. Generally,dispersions are prepared by incorporating the purified anti-ILT5antibody or ILT5-binding fragment into a sterile vehicle which containsa basic dispersion medium and the required other ingredients from thoseenumerated above. In the case of sterile powders for the preparation ofsterile injectable solutions, exemplary methods of preparation arevacuum drying and freeze-drying which yields a powder of the activeingredient plus any additional desired ingredient from a previouslysterile-filtered solution thereof.

Oral compositions generally include an inert diluent or an ediblecarrier. For the purpose of oral therapeutic administration, ananti-ILT5 antibody or an ILT5-binding antibody fragment can beincorporated with excipients and used in the form of tablets, troches,or capsules, e.g., gelatin capsules. Oral compositions can also beprepared using a fluid carrier for use as a mouthwash. Pharmaceuticallycompatible binding agents, and/or adjuvant materials can be included aspart of the composition. The tablets, pills, capsules, troches and thelike can contain any of the following ingredients, or compounds of asimilar nature: a binder such as microcrystalline cellulose, gumtragacanth or gelatin; an excipient such as starch or lactose, adisintegrating agent such as alginic acid, Primogel, or corn starch; alubricant such as magnesium stearate or Sterotes; a glidant such ascolloidal silicon dioxide; a sweetening agent such as sucrose orsaccharin; or a flavoring agent such as peppermint, methyl salicylate,or orange flavoring. Formulations for oral delivery may advantageouslyincorporate agents to improve stability within the gastrointestinaltract and/or to enhance absorption.

For administration by inhalation, an anti-ILT5 antibody or anILT5-binding antibody fragment and a delivery agent are preferablydelivered in the form of an aerosol spray from a pressured container ordispenser which contains a suitable propellant, e.g., a gas such ascarbon dioxide, or a nebulizer. The present disclosure particularlycontemplates delivery of the compositions using a nasal spray, inhaler,or other direct delivery to the upper and/or lower airway. Intranasaladministration of DNA vaccines directed against influenza viruses hasbeen shown to induce CD8 T cell responses, indicating that at least somecells in the respiratory tract can take up DNA when delivered by thisroute, and the delivery agents of the invention will enhance cellularuptake. According to certain embodiments, an anti-ILT5 antibody orILT5-binding fragment thereof and a delivery agent are formulated aslarge porous particles for aerosol administration.

Systemic administration can also be by transmucosal or transdermalmeans. For transmucosal or transdermal administration, penetrantsappropriate to the barrier to be permeated are used in the formulation.Such penetrants are generally known in the art, and include, forexample, for transmucosal administration, detergents, bile salts, andfusidic acid derivatives. Transmucosal administration can beaccomplished through the use of nasal sprays or suppositories. Fortransdermal administration, the purified polypeptide or protein anddelivery agents are formulated into ointments, salves, gels, or creamsas generally known in the art.

In certain embodiments, compositions are prepared with carriers thatwill protect an anti-ILT5 antibody or an ILT5-binding antibody fragmentagainst rapid elimination from the body, such as a controlled releaseformulation, including implants and microencapsulated delivery systems.Biodegradable, biocompatible polymers can be used, such as ethylenevinyl acetate, polyanhydrides, polyglycolic acid, collagen,polyorthoesters, and polylactic acid. Methods for preparation of suchformulations will be apparent to those skilled in the art. The materialscan also be obtained commercially from Alza Corporation and NovaPharmaceuticals, Inc. Liposomal suspensions (including liposomestargeted to infected cells with monoclonal antibodies to viral antigens)can also be used as pharmaceutically acceptable carriers. These can beprepared according to methods known to those skilled in the art, forexample, as described in U.S. Pat. No. 4,522,811, incorporated herein byreference in its entirety.

It is advantageous to formulate oral or parenteral compositions indosage unit form for ease of administration and uniformity of dosage.“Dosage unit form” as used herein refers to physically discrete unitssuited as unitary dosages for the subject to be treated; each unitcontaining a predetermined quantity of active anti-ILT5 antibody orILT5-binding fragment thereof calculated to produce the desiredtherapeutic effect in association with the required pharmaceuticalcarrier.

An anti-ILT5 antibody or an ILT5-binding antibody fragment can beadministered at various intervals and over different periods of time asrequired, e.g., one time per week for between about 1 to 10 weeks,between 2 to 8 weeks, between about 3 to 7 weeks, about 4, 5, or 6weeks, etc. Those skilled in the art will appreciate that certainfactors can influence the dosage and timing required to effectivelytreat a subject, including but not limited to the severity of thedisease or disorder, previous treatments, the general health and/or ageof the subject, and other diseases present. Generally, treatment of asubject with an anti-ILT5 antibody or an ILT5-binding antibody fragmentas described herein can include a single treatment or, in many cases,can include a series of treatments. It is furthermore understood thatappropriate doses may depend upon the potency of the anti-ILT5 antibodyor ILT5-binding fragment and may optionally be tailored to theparticular recipient, for example, through administration of increasingdoses until a preselected desired response is achieved. It is understoodthat the specific dose level for any particular animal subject maydepend upon a variety of factors including the activity of the specificpolypeptide or protein employed, the age, body weight, general health,gender, and diet of the subject, the time of administration, the routeof administration, the rate of excretion, any drug combination, and thedegree of expression or activity to be modulated.

Pharmaceutical formulations as described herein can be included in acontainer, pack, or dispenser together with instructions foradministration.

Detection and Diagnostic Assays

Given their ability to bind to ILT5, anti-ILT5 antibodies andILT5-binding antibody fragments can be used to detect ILT5 (e.g., in abiological sample, such as serum or plasma), using any of a variety ofimmunoassays including, but not limited to, enzyme linked immunosorbentassays (ELISAs), radioimmunoassays (RIAs), cell sorting assays (e.g.fluorescent activation cell sorting, or FACS), FCM or tissueimmunohistochemistry assays. In certain embodiments, methods fordetecting ILT5 (e.g., human ILT5) in a biological sample are provided,certain of such methods comprising contacting a biological sample (e.g.a cell or tissue such as blood) with an anti-ILT5 antibody orILT5-binding fragment thereof, and detecting either the anti-ILT5antibody or ILT5-binding fragment bound to ILT5 or unbound antibody orfragment, to thereby detect ILT5 in the biological sample. The anti-ILT5antibody or ILT5-binding fragment thereof may be directly or indirectlylabeled with a detectable label to facilitate detection of the bound orunbound anti-ILT5 antibody or ILT5-binding fragment. Suitable detectablelabels include various enzymes, prosthetic labels, fluorescent labels,luminescent labels and radioactive labels. Non-limiting examples ofsuitable enzymes include horseradish peroxidase, alkaline phosphatase,beta-galactosidase, and acetylcholinesterase. Non-limiting examples ofsuitable prosthetic labels include streptavidin/biotin andavidin/biotin. Non-limiting examples of suitable fluorescent labelsinclude umbelliferone, fluorescein, fluorescein isothiocyanate,rhodamine, dichlorotriazinylamine fluorescein, dansyl chloride orphycoerythrin. A non-limiting example of a luminescent label includesluminal. Non-limiting examples of suitable radioactive labels include¹²⁵I, ¹³¹I, ³⁵S and ³H.

In certain embodiments, ILT5 can be assayed in a biological sample by acompetition immunoassay utilizing ILT5 standards labeled with adetectable substance and an unlabeled anti-ILT5 antibody or ILT5-bindingfragment thereof. In such an assay, the biological sample, the labeledILT5 standards and the anti-ILT5 antibody or ILT5-binding fragment arecombined and the amount of labeled ILT5 standard bound to the anti-ILT5unlabeled antibody or ILT5-binding fragment is determined. The amount ofILT5 in the biological sample is inversely proportional to the amount oflabeled ILT5 standard bound to the anti-ILT5 antibody or ILT5-binding.

Other detection assays that utilize antibodies or fragments will beknown to those skilled in the art. Any of the antibodies or fragmentsdescribed herein may be used in accordance with such assays.

Cells

As described in the Examples below, culturing of human PBMCs andanti-ILT5 antibody resulted in the production in the cultures ofdistinct CD4+ and CD8+ T cells populations. Based on these findings,this disclosure provides the isolated or cultured cells described belowin this section.

In certain embodiments, a cell of the present disclosure is a human CD4⁺T cell that expresses CD25 and NKG2D (a CD4⁺CD25⁺NKG2D⁺ T cell). Incertain embodiments, a cell of the present disclosure is a human CD8⁺ Tcell that expresses CD25, and also expresses NKG2D at a level higherthan the level of NKG2D observed on steady state natural killer cells(CD8⁺CD25⁺ NKG2D^(hi) T cell). In certain embodiments, such human Tcells proliferate in a manner that does not require recognition of a MHCmolecule by the T cell, e.g., in a TCR-independent manner (e.g.,proliferation does not require recognition of a MHC molecule by a TCR).In certain embodiments, such human T cells secrete Fas ligand (FasL) ata higher level than a näive T cell. In certain embodiments, such T cellsexpress a TCR:CD3 complex at a higher level than would be observed on anäive T cell. In certain embodiments, such human T cells express MHCClass II (DR) at a higher level than would be observed on a näive Tcell.

In certain embodiments, a CD4⁺CD25⁺NKG2D⁺ or CD8⁺CD25+ NKG2D^(hi) T cellmaintains NKG2D on its cell surface under a condition in which the NKG2Dis typically internalized from the cell surface. Non-limiting examplesof such conditions include engagement of the NKG2D with an NKG2D ligandexpressed on the surface of a cell, engagement of the NKG2D with asecreted NKG2D ligand, and engagement of the NKG2D with an antibody orfragment that binds NKG2D.

In certain embodiments, a CD4⁺CD25⁺NKG2D⁺ or CD8⁺CD25⁺ NKG2D^(hi) T cellis produced by a method comprising contacting a näive T cell with anantigen presenting cell (APC) that has previously been contacted with ananti-ILT5 antibody or an ILT5-binding antibody fragment. In certainembodiments, a CD4⁺CD25⁺NKG2D⁺ or CD8⁺CD25⁺ NKG2D^(hi) T cell isproduced by a method comprising contacting a memory T cell with anantigen presenting cell (APC) that has previously been contacted with ananti-ILT5 antibody or an ILT5-binding fragment of the antibody in theabsence of TCR stimulation.

In certain embodiments, such a CD4⁺CD25⁺NKG2D⁺ or CD8⁺CD25⁺NKG2D^(hi) Tcell, or its progeny, is endowed with cytotoxic potential, as describedherein. In certain embodiments, a CD4⁺CD25⁺NKG2D⁺ or CD8⁺CD25⁺NKG2D^(hi) T cell is induced to become cytotoxic when it binds to orrecognizes an antigen. Binding or recognition with any of a variety ofantigens will result in the transition from having cytotoxic potentialto cytotoxicity. For example, a CD4⁺CD25+NKG2D⁺ or CD8⁺CD25⁺NKG2D^(hi) Tcell that exhibits cytotoxic potential may become cytotoxic when itbinds to or recognizes a purified or isolated antigen. Similarly, aCD4⁺CD25⁺NKG2D⁺ or CD8⁺CD25⁺NKG2D^(hi) T cell that exhibits cytotoxicpotential may become cytotoxic when it binds to or recognizes anunpurified or non-isolated antigen such as, for example, an antigenderived from a cellular lysate, or an antigen present in a blood orserum sample. In certain embodiments, a CD4⁺CD25⁺NKG2D⁺ or CD8+CD25⁺NKG2D^(hi) T cell having cytotoxic potential is induced to becomecytotoxic when the cell binds to or recognizes a cancerous cell, or acell that is infected with a bacterium, a virus, a fungus, a protozoan,or a parasite. In certain embodiments, a CD4⁺CD25⁺NKG2D⁺ or CD8⁺CD25⁺NKG2D^(hi) T cell having cytotoxic potential is induced to becomecytotoxic when the cell binds to or recognizes an antigen present on acancerous cell, or a cell that is infected with a bacterium, a virus, afungus, a protozoan, or a parasite.

In certain embodiments, in cell cultures comprising a CD4⁺CD25⁺NKG2D⁺ orCD8⁺CD25⁺ NKG2D^(hi) T cell the cytokines TNF-alpha (tumor necrosisfactor alpha) and IL5, and/or the chemokines, Rantes, IP-10(interferon-inducible protein 10), or MIP-1 (macrophage inflammatoryprotein 1) are produced. In certain embodiments, a CD4⁺CD25⁺NKG2D⁺ orCD8+CD25⁺ NKG2D^(hi) T cell present in such a cell culture produces oneor more of Rantes, IP-10, TNF-alpha, IL5, or MIP-1 itself. In certainembodiments, a CD4+CD25+NKG2D+ or CD8+CD25+ NKG2D^(hi) T cell in a cellculture induces another type of cell in the culture to produce one ormore of Rantes, IP-10, TNF-alpha, IL5, or MIP-1. For example, aCD4+CD25+NKG2D+ or CD8+CD25+ NKG2D^(hi) T cell can induce one or more ofa monocyte, a macrophage, a T cell other than CD4+CD25+NKG2D+ orCD8+CD25+ NKG2D^(hi) T cell, a B cell, a mast cell, an endothelial cell,and/or a fibroblast to produce one or more of Rantes, IP-10, TNF-alpha,IL5, or MIP-1. Thus, methods of using CD4+CD25+NKG2D+ or CD8+CD25+NKG2D^(hi) cells for inducing the production of these soluble mediators(cytokine and chemokines) by these cell types (monocytes, macrophages, Tcells other than CD4+CD25+NKG2D+ or CD8+CD25+NKG2D^(hi) T cells, or Bcells) are provided.

CD4⁺CD25⁺NKG2D⁺ or CD8⁺CD25⁺ NKG2D^(hi) T cells as described in thissection may be used in any of a variety of applications, including anyof the applications described in the section entitled “Treatment ofDiseases and Infections” above.

Anti-ILT5 Antibodies and ILT5-Binding Fragments Thereof

Disclosed herein are a variety of anti-ILT5 antibodies and ILT5-bindingantibody fragments thereof. In certain embodiments, an anti-ILT5antibody or an ILT5-binding antibody fragment thereof can be used forone or more applications described herein (e.g., inducing animmunostimulatory response in T cells, thereby causing them toproliferate or display a cytotoxic function). In certain embodiments,such T cells produce cytokines and/or induce other cells to producecytokines and/or chemokines. In certain embodiments, such T cells may beused in the treatment of various diseases or infections. In certainembodiments, the antibody is monoclonal. In certain embodiments, ananti-ILT5 antibody or an ILT5-binding antibody fragment is chimeric inthat it contains human heavy and/or light chain constant regions. See,for example, Cabilly et al., U.S. Pat. No. 4,816,567; Shoemaker et al.,U.S. Pat. No. 4,978,775; Beavers et al., U.S. Pat. No. 4,975,369; andBoss et al., U.S. Pat. No. 4,816,397, each of which is incorporatedherein by reference in its entirety. In certain embodiments, ananti-ILT5 antibody or ILT5-binding fragment thereof is humanized in thatit contains one or more human framework regions in the variable regiontogether with non-human (e.g., mouse, rat, or hamster)complementarity-determining regions (CDRs) of the heavy and/or lightchain. Humanized antibodies can be produced using recombinant DNAtechniques well known to those skilled in the art. See for example,Hwang, W. Y. K., et al., Methods 36:35, 2005; Queen et al., Proc. Natl.Acad. Sci. USA, 86:10029-10033, 1989; Jones et al., Nature, 321:522-25,1986; Riechmann et al., Nature, 332:323-27, 1988; Verhoeyen et al.,Science, 239:1534-36, 1988; Orlandi et al., Proc. Natl. Acad. Sci. USA,86:3833-37, 1989; U.S. Pat. Nos. 5,225,539; 5,530,101; 5,585,089;5,693,761; 5,693,762; 6,180,370; and Selick et al., WO 90/07861, each ofwhich is incorporated herein by reference in its entirety.

In certain embodiments, a fragment (e.g., an antigen-binding fragment)is derived from a whole antibody molecule, such as a monoclonal or apolyclonal antibody. The antibody can be, e.g., cleaved on the carboxyterminal side of its hinge region (e.g., with pepsin) to generate aF(ab′)₂ fragment, or on the amino terminal side of its hinge region(e.g., with papain) to generate Fab fragments. In certain embodiments,an anti-ILT5 antibody or an ILT5-binding antibody fragment binds humanILT5.

In certain embodiments, an anti-ILT5 antibody fragment is a Fabfragment, a F(ab′)₂ fragment, a scFv fragment, a diabody, a linearantibody, a multispecific antibody fragment such as a bispecific, atrispecific, or a multispecific antibody (e.g., a diabody, a triabody, atetrabody), a minibody, a chelating recombinant antibody, a tribody orbibody, an intrabody, a nanobody, a small modular immunopharmaceutical(SMIP), a binding-domain immunoglobulin fusion protein, a camelidantibody, or a V_(HH) containing antibody. Those skilled in the art willbe aware of how to engineer or construct such antibodies or fragmentswithout undue experimentation.

In certain embodiments, an anti-ILT5 antibody or an ILT5-bindingantibody fragment thereof comprises a light chain variable regioncomprising the amino acid sequence of SEQ ID NO: 1[DIQMTQSPASLSVSVGETVTITCRASENIYSNLAWYQQKQGKSPQVLVYAATNLADGVPSRFSGSGSGTQFSLKINSLQSEDFGNYFCQHFWRIPWTFGGGTKLEIK]. In certainembodiments, an anti-ILT5 antibody or an ILT5-binding antibody fragmentcomprises a heavy chain variable region comprising the amino acidsequence of SEQ ID NO: 2[DVQLQESGPGLVKPSQSLFLTCSVTGYSISSSYYWNWIRQFPGNKLEWMGYISFDGSNNYNPSLKNRISITRDTSKNQFFLKLNSVTTEDTATYYCAREKENYYGSSFYYFDYWGLGT SLTVSS]. Incertain embodiments, an anti-ILT5 antibody or an ILT5-binding antibodyfragment comprises a heavy chain variable region comprising the aminoacid sequence of SEQ ID NO: 3[EVQLQESGPGLVKPSQSLFLTCSVTGYSISSSYYWNWIRQFPGNKLEWMGYISFDGSNNYNPSLKNRISITRDTSKNQFFLKLNSVTTEDTATYYCAREKENYYGSSFYYFDYWGLGT SLTVSS].

In certain embodiments, an anti-ILT5 antibody or ILT5-binding fragmentthereof comprises a light chain variable region comprising the aminoacid sequence of SEQ ID NO: 1 and a heavy chain variable regioncomprising the amino acid sequence of SEQ ID NO: 2. In certainembodiments, an anti-ILT5 antibody or ILT5-binding fragment thereofcomprises a light chain variable region comprising the amino acidsequence of SEQ ID NO: 1 and a heavy chain variable region comprisingthe amino acid sequence of SEQ ID NO: 3.

In certain embodiments, an anti-ILT5 antibody or an ILT5-bindingantibody fragment, e.g., a humanized or chimeric antibody or fragment,comprises one or more of the following CDRs: SEQ ID NO: 4 [SSYYWN](VHCDR1), SEQ ID NO: 5 [YISFDGSNNYNPSLKN](VH CDR2), SEQ ID NO: 6[EKENYYGSSFYYFDY](VH CDR3), SEQ ID NO: 7 [RASENIYSNLA](VL CDR1), SEQ IDNO: 8 [AATNLAD](VL CDR2), and SEQ ID NO: 9 [QHFWRIPWT](VL CDR3).

In certain embodiments, an anti-ILT5 antibody or an ILT5-bindingantibody fragment, e.g., a humanized or chimeric antibody or fragment,comprises a heavy chain variable region (VH) comprising: a VH CDR1comprising the amino acid sequence of SEQ ID NO: 4, a VH CDR2 comprisingthe amino acid sequence of SEQ ID NO: 5, and a VH CDR3 comprising theamino acid sequence of SEQ ID NO: 6. In certain embodiments, ananti-ILT5 antibody or ILT5-binding fragment thereof, e.g., a humanizedor chimeric antibody or fragment, comprises a light chain variableregion (VL) comprising: a VL CDR1 comprising the amino acid sequence ofSEQ ID NO: 7, a VL CDR2 comprising the amino acid sequence of SEQ ID NO:8, and a VL CDR3 comprising the amino acid sequence of SEQ ID NO: 9. Incertain embodiments, an anti-ILT5 antibody or an ILT5-binding antibodyfragment, e.g., a humanized or chimeric antibody or fragment, comprisesa heavy chain variable region comprising: a VH CDR1 comprising the aminoacid sequence of SEQ ID NO: 4, a VH CDR2 comprising the amino acidsequence of SEQ ID NO: 5, a VH CDR3 comprising the amino acid sequenceof SEQ ID NO: 6, a VL CDR1 comprising the amino acid sequence of SEQ IDNO: 7, a VL CDR2 comprising the amino acid sequence of SEQ ID NO: 8, anda VL CDR3 comprising the amino acid sequence of SEQ ID NO: 9.

In certain embodiments, an anti-ILT5 antibody or an ILT5-bindingantibody fragment comprises a heavy chain variable region comprising: aVH CDR1 consisting of the amino acid sequence of SEQ ID NO: 4, a VH CDR2consisting of the amino acid sequence of SEQ ID NO: 5, and a VH CDR3consisting of the amino acid sequence of SEQ ID NO: 6. In certainembodiments, an anti-ILT5 antibody or an ILT5-binding antibody fragmentcomprises a light chain variable region comprising: a VL CDR1 consistingof the amino acid sequence of SEQ ID NO: 7, a VL CDR2 consisting of theamino acid sequence of SEQ ID NO: 8, and a VL CDR3 consisting of theamino acid sequence of SEQ ID NO: 9.

In certain embodiments, an anti-ILT5 antibody or an ILT5-bindingantibody fragment comprises a heavy chain variable region comprising: aVH CDR1 comprising the amino acid sequence of SEQ ID NO: 4, a VH CDR2comprising the amino acid sequence of SEQ ID NO: 5, a VH CDR3 comprisingthe amino acid sequence of SEQ ID NO: 6, a VL CDR1 consisting of theamino acid sequence of SEQ ID NO: 7, a VL CDR2 consisting of the aminoacid sequence of SEQ ID NO: 8, and a VL CDR3 consisting of the aminoacid sequence of SEQ ID NO: 9. In certain embodiments, an anti-ILT5antibody or an ILT5-binding antibody fragment comprises a heavy chainvariable region comprising: a VH CDR1 consisting of the amino acidsequence of SEQ ID NO: 4, a VH CDR2 consisting of the amino acidsequence of SEQ ID NO: 5, a VH CDR3 consisting of the amino acidsequence of SEQ ID NO: 6, a VL CDR1 comprising the amino acid sequenceof SEQ ID NO: 7, a VL CDR2 comprising the amino acid sequence of SEQ IDNO: 8, and a VL CDR3 comprising the amino acid sequence of SEQ ID NO: 9.In certain embodiments, an anti-ILT5 antibody or an ILT5-bindingantibody fragment thereof comprises a heavy chain variable regioncomprising: a VH CDR1 consisting of the amino acid sequence of SEQ IDNO: 4, a VH CDR2 consisting of the amino acid sequence of SEQ ID NO: 5,a VH CDR3 consisting of the amino acid sequence of SEQ ID NO: 6, a VLCDR1 consisting of the amino acid sequence of SEQ ID NO: 7, a VL CDR2consisting of the amino acid sequence of SEQ ID NO: 8, and a VL CDR3consisting of the amino acid sequence of SEQ ID NO: 9.

In certain embodiments, an anti-ILT5 antibody or an ILT5-bindingantibody fragment thereof is humanized in that it comprises one or morehuman framework regions, e.g. a human heavy chain framework regionand/or a human light chain framework region. In certain embodiments, ananti-ILT5 antibody or an ILT5-binding antibody fragment comprises one ormore human framework regions from a heavy chain variable regioncomprising an amino acid sequence selected from the group consisting ofthe amino acid sequence of SEQ ID NO: 10[QVQLQESGPGLVKPPGTLSLTCAVSGGSISSSYYWNWVRQPPGKGLEWIGYISFDGSNNYNPSLKNRVTISVDKSKNQFSLKLSSVTAADTAVYCCAREKENYYGSSFYYFDYWGQG TLVTVSS], SEQID NO: 11 [QVQLQESGPGLVKPSGTLSLTCAVSGGSISSSYYWNWVRQPPGKGLEWIGYISFDGSNNYNPSLKNRVTISVDKSKNQFSLKLSSVTAADTAVYCCAREKENYYGSSFYYFDYWGQG TLVTVSS], SEQID NO: 12 [QVQLQESGPGLVKPPGTLSLTCAVSGGSISSSYYWNWVRQPPGKGLEWIGYISFDGSNNYNPSLKNRVTISVDKSKNQFSLKLSSVTAADTAVYYCAREKENYYGSSFYYFDYWGQG TLVTVSS], SEQID NO: 13 [QVQLQESGPGLVKPSDTLSLTCAVSGYSISSSYYWNWIRQPPGKGLEWIGYISFDGSNNYNPSLKNRVTMSVDTSKNQFSLKLSSVTAVDTAVYYCAREKENYYGSSFYYFDYWGQ GTLVTVSS], SEQID NO: 14 [QLQLQESGPGLVKPSETLSLTCTVSGGSISSSYYWNWIRQPPGKGLEWIGYISFDGSNNYNPSLKNRVTISVDTSKNQFSLKLSSVTAADTAVYYCAREKENYYGSSFYYFDYWGQGT LVTVSS], SEQID NO: 15 [QVQLQESGPGLVKPSETLSLTCTVSGGSISSSYYWNWIRQPPGKGLEWIGYISFDGSNNYNPSLKNRVTISVDTSKNQFSLKLSSVTAADTAVYYCAREKENYYGSSFYYFDYWGQGT LVTVSS], SEQID NO: 16 [QVQLQESGPGLVKPSETLSLTCTVSGGSVSSSYYWNWIRQPPGKGLEWIGYISFDGSNNYNPSLKNRVTISVDTSKNQFSLKLSSVTAADTAVYYCAREKENYYGSSFYYFDYWGQG TLVTVSS], andSEQ ID NO: 17[QVQLQESGPGLVKPSETLSLTCAVSGYSISSSYYWNWIRQPPGKGLEWIGYISFDGSNNYNPSLKNRVTISVDTSKNQFSLKLSSVTAADTAVYYCAREKENYYGSSFYYFDYWGQG TLVTVSS](CDRsequences are underlined in SEQ ID NOs: 10-17, while framework regionslack underlining. The four framework regions in each sequence arenumbered 1-4 (FW1, FW2, FW3, and FW4) starting from the N-terminal endsof the sequences). In certain embodiments, an anti-ILT5 antibody or anILT5-binding antibody fragment comprises one or more human frameworkregions from a heavy chain variable region comprising an amino acidsequence selected from the group consisting of the amino acid sequenceof SEQ ID NO: 10.

In certain embodiments, an anti-ILT5 antibody or an ILT5-bindingantibody fragment comprises one or more human framework regions from alight chain variable region comprising an amino acid sequence selectedfrom the group consisting of the amino acid sequence of SEQ ID NO: 18[AIRMTQSPSSFSASTGDRVTITCRASENIYSNLAWYQQKPGKAPKLLIYAATNLADGVPSRFSGSGSGTDFTLTISCLQSEDFATYYFATYYCQHFWRIPWTFGQGTKVEIK], SEQ ID NO: 19[DIQLTQSPSFLSASVGDRVTITCRASENIYSNLAWYQQKPGKAPKLLIYAATNLADGVPSRFSGSGSGTEFTLTISSLQPEDFATYYCQHFWRIPWTFGQGTKVEIK], SEQ ID NO: 20[DIQMTQSPSSVSASVGDRVTITCRASENIYSNLAWYQQKPGKAPKLLIYAATNLADGVPSRFSGSGSGTDFTLTISSLQPEDFATYYCQHFWRIPWTFGQGTKVEIK], SEQ ID NO: 21[DIQMTQSPSSVSASVGDRVTITCRASENIYSNLAWYQQKPGKAPKLLIYAATNLADGVPSRFSGSGSGTDFTLTISSLQPEDFATYYCQHFWRIPWTFGQGTKVEIK], SEQ ID NO: 22[AIQLTQSPSSLSASVGDRVTITCRASENIYSNLAWYQQKPGKAPKLLIYAATNLADGVPSRFSGSGSGTDFTLTISSLQPEDFATYYCQHFWRIPWTFGQGTKVEIK], SEQ ID NO: 23[AIQLTQSPSSLSASVGDRVTITCRASENIYSNLAWYQQKPGKAPKLLIYAATNLADGVPSRFSGSGSGTDFTLTISSLQPEDFATYYCQHFWRIPWTFGQGTKVEIK], and SEQ ID NO: 24[DIQMTQSPSSLSASVGDRVTITCRASENIYSNLAWYQQKPEKAPKSLIYAATNLADGVPSRFSGSGSGTDFTLTISSLQPEDFATYYCQHFWRIPWTFGQGTKVEIK](CDR sequences areunderlined in SEQ ID NOs: 18-24, while framework regions lackunderlining. The four framework regions in each sequence are numbered1-4 (FW1, FW2, FW3, and FW4) starting from the N-terminal ends of thesequences). In certain embodiments, an anti-ILT5 antibody or anILT5-binding antibody fragment thereof comprises one or more humanframework regions from a light chain variable region comprising an aminoacid sequence selected from the group consisting of the amino acidsequence of SEQ ID NO: 18.

In certain embodiments, an anti-ILT5 antibody or an ILT5-bindingantibody fragment comprises one or more human framework regions from aheavy chain variable region comprising an amino acid sequence selectedfrom the group consisting of the amino acid sequence of SEQ ID NO:10-17, and a light chain variable region comprising an amino acidsequence selected from the group consisting of the amino acid sequenceof SEQ ID NOs: 18-24.

In certain embodiments, a CDR homology based method is used forhumanization (see, e.g., Hwang, W. Y. K., et al., Methods 36:35, 2005).This method generally involves substitution of non-human CDRs into ahuman framework based on similarly structured non-human and human CDRs,rather than similarly structured non-human and human frameworks. Thesimilarity of the non-human and human CDRs is generally determined byidentifying human genes of the same chain type (light or heavy) thathave the same combination of canonical CDR structures as the mousebinding molecules and thus retain three-dimensional conformation of CDRpeptide backbones. Secondly, for each of the candidate variable regiongene segments with matching canonical structures, residue to residuehomology between the non-human and candidate human CDRs is evaluated.Finally, to generate a humanized binding molecule, CDR residues of thechosen human candidate CDR not already identical to the non-human CDRare converted to the non-human sequence. In certain embodiments, nomutations of the human framework are introduced into the humanizedbinding molecule.

In certain embodiments, the substitution of non-human CDRs into a humanframework is based on the retention of the correct spatial orientationof the non-human framework by identifying human frameworks which willretain the same conformation as the non-human frameworks from which theCDRs were derived. In certain embodiments, this is achieved by obtainingthe human variable regions from human antibodies whose frameworksequences exhibit a high degree of sequence identity with the non-humanframework regions from which the CDRs were derived. See Kettleborough etal., Protein Engineering 4:773, 1991; Kolbinger et al., ProteinEngineering 6:971, 1993; and Carter et al., WO 92/22653, each of whichis incorporated herein by reference in its entirety.

In certain embodiments, one or more human framework residues can bechanged or substituted to residues at the corresponding positions in theoriginal non-human (e.g. murine) antibody so as to preserve the bindingaffinity of the humanized antibody to the antigen. Such a change issometimes called “backmutation”. Certain amino acids from the humanframework residues are selected for backmutation based on their possibleinfluence on CDR conformation and/or binding to antigen. For example,residues immediately surrounding one or more CDRs can be backmutated toensure proper spatial positioning of the CDRs. The placement ofnon-human (e.g. murine) CDR regions within human framework regions canresult in conformational restraints, which, unless corrected bysubstitution of certain amino acid residues, lead to loss of bindingaffinity. Thus, in certain embodiments, backmutations can be made inresidues that affect proper conformation of the anti-ILT5 antibody orILT5-binding fragment to ensure adequate affinity to ILT5.

In certain embodiments, the selection of amino acid residues forbackmutation can be determined, in part, by computer modeling, using artrecognized techniques. In general, molecular models are producedstarting from solved structures for immunoglobulin chains or domainsthereof. The chains to be modeled are compared for amino acid sequencesimilarity with chains or domains of solved three-dimensionalstructures, and the chains or domains showing the greatest sequencesimilarity is/are selected as starting points for construction of themolecular model. Chains or domains sharing at least 50% sequenceidentity are selected for modeling, and preferably those sharing atleast 60%, 70%, 80%, 90% sequence identity or more are selected formodeling. The solved starting structures are modified to allow fordifferences between the actual amino acids in the immunoglobulin chainsor domains being modeled, and those in the starting structure. Themodified structures are then assembled into a composite immunoglobulin.Finally, the model is refined by energy minimization and by verifyingthat all atoms are within appropriate distances from one another andthat bond lengths and angles are within chemically acceptable limits.

The selection of amino acid residues for substitution can also bedetermined, in part, by examination of the characteristics of the aminoacids at particular locations, or empirical observation of the effectsof substitution or mutagenesis of particular amino acids. For example,when an amino acid differs between a non-human (e.g. murine) frameworkresidue and a selected human framework residue, the human frameworkamino acid may be substituted by the equivalent framework amino acidfrom the non-human binding molecule when it is reasonably expected thatthe amino acid: (1) noncovalently binds antigen directly, (2) isadjacent to a CDR region, (3) otherwise interacts with a CDR region(e.g., is within about 3-6 angstroms of a CDR region as determined bycomputer modeling), or (4) participates in the VL-VH interface.

In certain embodiments, an anti-ILT5 antibody or an ILT5-bindingantibody fragment comprises a human heavy chain constant region. Forexample, an anti-ILT5 antibody or an ILT5-binding antibody fragment maycomprise an IgG (γ) heavy chain constant region such as a IgG1 (γ1)heavy chain constant region, an IgG2 (γ2) heavy chain constant region,an IgG3 (γ3) heavy chain constant region, or an IgG4 (γ4) heavy chainconstant region. Moreover, they can comprise an IgA (α) heavy chainconstant region, an IgE (ε) heavy chain constant region, an IgM (μ)heavy chain constant region, or an IgD (δ) heavy chain constant region.In certain embodiments, an anti-ILT5 antibody or an ILT5-bindingantibody fragment comprises a heavy chain constant region comprising theamino acid sequence of SEQ ID NO: 25[ASTKGPSVFPLAPSSKSTSGGTAALGCLVKDYFPEPVTVSWNSGALTSGVHTFPAVLQSSGLYSLSSVVTVPSSSLGTQTYICNVNHKPSNTKVDKKVEPKSCDKTHTCPPCPAPELLGGPSVFLFPPKPKDTLMISRTPEVTCVVVDVSHEDPEVKFNWYVDGVEVHNAKTKPREEQYNSTYRVVSVLTVLHQDWLNGKEYKCKVSNKALPAPIEKTISKAKGQPREPQVYTLPPSRDELTKNQVSLTCLVKGFYPSDIAVEWESNGQPENNYKTTPPVLDSDGSFFLYSKLTVDKSRWQQGNVFSCSVMHEALHNHYTQKSLSLSPGK]. In certain embodiments, ananti-ILT5 antibody or an ILT5-binding antibody fragment comprises aheavy chain constant region comprising the amino acid sequence of SEQ IDNO: 26 [ASTKGPSVFPLAPSSKSTSGGTAALGCLVKDYFPEPVTVSWNSGALTSGVHTFPAVLQSSGLYSLSSVVTVPSSSLGTQTYICNVNHKPSNTKVDKKVEPKSCDKTHTCPPCPAPELLGGPSVFLFPPKPKDTLMISRTPEVTCVVVDVSHEDPEVKFNWYVDGVEVHNAKTKPREEQYASTYRVVSVLTVLHQDWLNGKEYKCKVSNKALPAPIEKTISKAKGQPREPQVYTLPPSRDELTKNQVSLTCLVKGFYPSDIAVEWESNGQPENNYKTTPPVLDSDGSFFLYSKLTVDKSRWQQGNVFSCSVMHEALHNHYTQKSLSLSPGK]. SEQ ID NO: 26 differs from SEQ IDNO: 25 in that an asparagine has been altered to an alanine (therelevant amino acid is underlined in each sequence), which alterationresults in elimination of N-linked in vivo glycosylation of anti-ILT5antibodies and ILT5-binding fragments thereof comprising SEQ ID NO: 26.Absence of N-linked glycosylation at the relevant residue results indrastically decreased binding of the Fc region of the relevant anti-ILT5antibody or ILT5-binding fragment to a Fc receptor.

Any of a variety of other modifications may be made that result inreduced binding of an anti-ILT5 antibody or an ILT5-binding fragment toa Fc receptor. For example, a humanized OTK3-derived antibody in whichtwo amino acid residues at positions 234 and 235 of the Fc domain havebeen modified to alanine residues (referred to as hOKT3-gamma-1(ala-ala)) is disclosed in United States Patent Publication numbers2007/0077246 and 2008/0095766, the disclosures of which are incorporatedherein by reference in their entirety. The hOKT3-gamma-1 (ala-ala)antibody is described as exhibiting reduced binding to Fc (gamma)receptors, even though its Fc domain comprises residues that areN-linked glycosylated. In certain embodiments, an ant-ILT5 antibody oran ILT5-binding fragment thereof that exhibits reduced binding to atleast one Fc (gamma) receptor is modified in that it lacks some or allof an Fc domain. For example, Fab fragments and F(ab′)₂ fragments lacksome or all of an Fc domain. In certain embodiments, an antibody orantigen-binding fragment thereof is modified in some other way such thatit exhibits reduced binding to at least one Fc (gamma) receptor. Forexample, the anti-ILT5 antibody or ILT5-binding fragment may be modifiedby covalent linkage of a chemical moiety that prevents the anti-ILT5antibody or ILT5-binding fragmen from binding, or decreases its abilityto bind, to least one Fc (gamma) receptor. As another example, theanti-ILT5 antibody or ILT5-binding fragment may be modified bynon-covalent linkage of a chemical moiety that prevents the anti-ILT5antibody or ILT5-binding fragment from binding, or decreases its abilityto bind, to least one Fc (gamma) receptor. Any of a variety of moietiesmay be covalently or non-covalently linked to the anti-ILT5 antibody orILT5-binding fragment thereof to prevent or decrease binding to at leastone Fc (gamma) receptor. Those skilled in the art will be aware ofsuitable moieties that can be linked to an antibody or fragment, andwill be able to employ such moieties in accordance with the teachingsherein.

In certain embodiments, any of a variety of modifications may be made toan anti-ILT5 antibody or an ILT5-binding antibody fragment, whichmodification results in alteration of the a physical or in vivo propertyof the anti-ILT5 antibody or ILT5-binding fragment. For example, any ofa variety of modifications may be made that affect the stability of theanti-ILT5 antibody or ILT5-binding fragment (e.g., in vivo).Additionally and/or alternatively, any of a variety of modifications maybe made that affect the halflife of an anti-ILT5 antibody orILT5-binding fragment thereof in vivo. As is known in the art, FcRnprotects IgG-type antibodies from degradation, resulting in longerhalf-life of this class of antibody in the serum (see Roopenian andAkilesh, Nature Reviews Immunology 7, 715-725, 2007, incorporated hereinby reference in its entirety). Thus, in certain embodiments, an IgG-typeantiI-ILT5 antibody or fragment thereof is modified by altering aminoacid residues in its Fc region such that it bind differently to FcRn.Alterations that result in improved binding to FcRn will result in theanti-ILT5 antibody or ILT5-binding fragment having a longer halflife invivo. Alterations that result in decreased binding to FcRn will resultin the anti-ILT5 antibody or ILT5-binding fragment having a shorterhalflife in vivo. Those skilled in the art will be aware of suitablealterations that can be made, such as pegylation and/or amino acidsubstitutions, and will be able to make such corresponding alterationsin anti-ILT5 antibodies and ILT5-binding fragments thereof disclosedherein without undue experimentation.

In certain embodiments, an anti-ILT5 antibody or an ILT5-bindingantibody fragment comprises a human light chain constant region. Forexample, an anti-ILT5 antibody or an ILT5-binding antibody fragment maycomprise a human kappa or human lambda light chain constant region. Incertain embodiments, an anti-ILT5 antibody or an ILT5-binding antibodyfragment comprises a light chain constant region comprising the aminoacid sequence of SEQ ID NO: 27[RTVAAPSVFIFPSDEQLKSGTASVVCLLNNFYPREAKVQWKVDNALQSGNSQESVTEQDSKDSTYSLSSTLTLSKADYEKHKVYACEVTHQGLSSPVTKSFNRGEC].

In certain embodiments, an anti-ILT5 antibody or an ILT5-bindingantibody fragment comprises a light chain comprising or consisting ofthe amino acid sequence of SEQ ID NO: 28[DIQMTQSPASLSVSVGETVTITCRASENIYSNLAWYQQKQGKSPQVLVYAATNLADGVPSRFSGSGSGTQFSLKINSLQSEDFGNYFCQHFWRIPWTFGAGTKLEIKRTVAAPSVFIFPPSDEQLKSGTASVVCLLNNFYPREAKVQWKVDNALQSGNSQESVTEQDSKDSTYSLSSTLTLSKADYEKHKVYACEVTHQGLSSPVTKSFNRGEC].

In certain embodiments, an anti-ILT5 antibody or an ILT5-bindingantibody fragment comprises a heavy chain comprising or consisting ofthe amino acid sequence of SEQ ID NO: 29[DVQLQESGPGLVKPSQSLFLTCSVTGYSISSSYYWNWIRQFPGNKLEWMGYISFDGSNNYNPSLKNRISITRDTSKNQFFLKLNSVTTEDTATYYCAREKENYYGS SFYYFDYWGAGTLVTVSSASTKGPSVFPLAPSSKSTSGGTAALGCLVKDYFPEPVTVSWNSGALTSGVHTFPAVLQSSGLYSLSSVVTVPSSSLGTQTYICNVNHKPSNTKVDKKVEPKSCDKTHTCPPCPAPELLGGPSVFLFPPKPKDTLMISRTPEVTCVVVDVSHEDPEVKFNWYVDGVEVHNAKTKPREEQYNSTYRVVSVLTVLHQDWLNGKEYKCKVSNKALPAPIEKTISKAKGQPREPQVYTLPPSRDELTKNQVSLTCLVKGFYPSDIAVEWESNGQPENNYKTTPPVLDSDGSFFLYSKLTVDKSRWQQGNVFSCSVMHEALHNHYTQKSLSLSPGK] or SEQ ID NO: 30:[EVQLQESGPGLVKPSQSLFLTCSVTGYSISSSYYWNWIRQFPGNKLEWMGYISFDGSNNYNPSLKNRISITRDTSKNQFFLKLNSVTTEDTATYYCAREKENYYGSSFYYFDYWGAGTLVTVSSASTKGPSVFPLAPSSKSTSGGTAALGCLVKDYFPEPVTVSWNSGALTSGVHTFPAVLQSSGLYSLSSVVTVPSSSLGTQTYICNVNHKPSNTKVDKKVEPKSCDKTHTCPPCPAPELLGGPSVFLFPPKPKDTLMISRTPEVTCVVVDVSHEDPEVKFNWYVDGVEVHNAKTKPREEQYNSTYRVVSVLTVLHQDWLNGKEYKCKVSNKALPAPIEKTISKAKGQPREPQVYTLPPSRDELTKNQVSLTCLVKGFYPSDIAVEWESNGQPENNYKTTPPVLDSDGSFFLYSKLTVDKSRWQQGNVFSCSVMHEALHNHYTQKSLSLSPGK]. In certain embodiments, ananti-ILT5 antibody or an ILT5-binding antibody fragment comprises aheavy chain comprising or consisting of the amino acid sequence of SEQID NO: 31 [DVQLQESGPGLVKPSQSLFLTCSVTGYSISSSYYWNWIRQFPGNKLEWMGYISFDGSNNYNPSLKNRISITRDTSKNQFFLKLNSVTTEDTATYYCAREKENYYGSSFYYFDYWGAGTLVTVSSASTKGPSVFPLAPSSKSTSGGTAALGCLVKDYFPEPVTVSWNSGALTSGVHTFPAVLQSSGLYSLSSVVTVPSSSLGTQTYICNVNHKPSNTKVDKKVEPKSCDKTHTCPPCPAPELLGGPSVFLFPPKPKDTLMISRTPEVTCVVVDVSHEDPEVKFNWYVDGVEVHNAKTKPREEQYASTYRVVSVLTVLHQDWLNGKEYKCKVSNKALPAPIEKTISKAKGQPREPQVYTLPPSRDELTKNQVSLTCLVKGFYPSDIAVEWESNGQPENNYKTTPPVLDSDGSFFLYSKLTVDKSRWQQGNVFSCSVMHEALHNHYTQKSLSLSPGK] or SEQ ID NO: 32[EVQLQESGPGLVKPSQSLFLTCSVTGYSISSSYYWNWIRQFPGNKLEWMGYISFDGSNNYNPSLKNRISITRDTSKNQFFLKLNSVTTEDTATYYCAREKENYYGSSFYYFDYWGAGTLVTVSSASTKGPSVFPLAPSSKSTSGGTAALGCLVKDYFPEPVTVSWNSGALTSGVHTFPAVLQSSGLYSLSSVVTVPSSSLGTQTYICNVNHKPSNTKVDKKVEPKSCDKTHTCPPCPAPELLGGPSVFLFPPKPKDTLMISRTPEVTCVVVDVSHEDPEVKFNWYVDGVEVHNAKTKPREEQYASTYRVVSVLTVLHQDWLNGKEYKCKVSNKALPAPIEKTISKAKGQPREPQVYTLPPSRDELTKNQVSLTCLVKGFYPSDIAVEWESNGQPENNYKTTPPVLDSDGSFFLYSKLTVDKSRWQQGNVFSCSVMHEALHNHYTQKSLSLSPGK]. SEQ ID NOs: 29 and 30 differsfrom SEQ ID NOs: 31 and 32 in that an asparagine has been altered to analanine (the relevant amino acid is underlined in each sequence), whichalteration results in decreased in vivo glycosylation of anti-ILT5antibodies and ILT5-binding fragments thereof comprising SEQ ID NOs: 31and 32.

In certain embodiments, an anti-ILT5 antibody or an ILT5-bindingantibody fragment comprises a light chain comprising or consisting ofthe amino acid sequence of SEQ ID NO: 28, and a heavy chain comprisingor consisting of the amino acid sequence of SEQ ID NO: 29, SEQ ID NO:30, SEQ ID NO: 31, or SEQ ID NO: 32.

In certain embodiments, an anti-ILT5 antibody or an ILT5-bindingantibody fragment comprises an amino acid sequence that is at least 75%identical to one or more of SEQ ID NOs: 1-32, e.g., at least 80%identical, at least 85% identical, at least 90% identical, at least 95%identical, at least 96% identical, at least 97% identical, at least 98%identical, or at least 99% identical to one or more of SEQ ID NOs: 1-32.In certain embodiments, an anti-ILT5 antibody or ILT5-binding fragmentthereof comprises an amino acid sequence comprising at least 5contiguous amino acid residues of one or more of SEQ ID NOs: 1-32, e.g.,at least 6, at least 7, at least 8, at least 9, at least 10, at least11, at least 12, at least 13, at least 14, at least 15, at least 20, atleast 25, at least 30, at least 40, at least 50, or more contiguousamino acid residues.

In certain embodiments, an anti-ILT5 antibody or an ILT5-bindingantibody fragment comprises a polypeptide having one or more amino acidsubstitutions, deletions or insertions as compared to a polypeptidehaving an amino acid sequence of one or more of SEQ ID NOs: 1-32. Forexample, an anti-ILT5 antibody or an ILT5-binding antibody fragment mayhave 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, or more amino acid substitutions,deletions or insertions. Substitutions, deletions or insertions may beintroduced by standard techniques, such as site-directed mutagenesis orPCR-mediated mutagenesis of a nucleic acid molecule encoding apolypeptide of an anti-ILT5 antibody or an ILT5-binding antibodyfragment. In certain embodiments, conservative amino acid substitutionsare made at one or more positions. A “conservative amino acidsubstitution” is one in which the amino acid residue is replaced with anamino acid residue having a similar side chain. Families of amino acidresidues having similar side chains have been defined in the art,including basic side chains (e.g., lysine, arginine, histidine), acidicside chains (e.g., aspartic acid, glutamic acid), uncharged polar sidechains (e.g., glycine, asparagine, glutamine, serine, threonine,tyrosine, cysteine), nonpolar side chains (e.g., alanine, valine,leucine, isoleucine, proline, phenylalanine, methionine, tryptophan),beta-branched side chains (e.g., threonine, valine, isoleucine) andaromatic side chains (e.g., tyrosine, phenylalanine, tryptophan;histidine). Thus, an amino acid residue in a polypeptide of an anti-ILT5antibody or an ILT5-binding antibody fragment may be replaced withanother amino acid residue from the same side chain family. In certainembodiments, a string of amino acids can be replaced with a structurallysimilar string that differs in order and/or composition of side chainfamily members. Those skilled in the art will be able to evaluatewhether an anti-ILT5 antibody or an ILT5-binding antibody fragmentcomprising a polypeptide having one or more amino acid substitutions,deletions or insertions as compared to a polypeptide having an aminoacid sequence of one or more of SEQ ID NOs: 1-32 binds ILT5 by utilizingroutine, art-recognized methods including, but not limited to, ELISAs,Western blots, phage display, etc.

Anti-ILT5 antibodies and ILT5-binding fragments thereof can be producedby any of a variety of methods known to those skilled in the art. Incertain embodiments, anti-ILT5 antibodies and ILT5-binding antibodyfragments can be produced recombinantly. For example, nucleic acidsequences encoding one or more of SEQ ID NOs: 1-32, or portions thereof,may be introduced into a bacterial cell (e.g., E. coli, B. subtilis) ora eukaryotic cell (e.g., a yeast such as S. cerevisiae, or a mammaliancell such as a CHO cell line, various Cos cell lines, a HeLa cell,various myeloma cell lines, or a transformed B-cell or hybridoma), orinto an in vitro translation system, and the translated polypeptide maybe isolated. One of ordinary skill in the art will recognize thatantibody light chain proteins and heavy chain proteins are produced inthe cell with a leader sequence that is removed upon production of amature anti-ILT5 antibody or ILT5-binding fragment thereof.

Anti-ILT5 antibodies and ILT5-binding antibody fragments can be preparedby recombinant expression of immunoglobulin light and heavy chain genesin a host cell. For example, a host cell is transfected with one or morerecombinant expression vectors carrying DNA fragments encoding the lightand heavy chains of the anti-ILT5 antibody or ILT5-binding fragment suchthat the light and heavy chains are expressed in the host cell and,preferably, secreted into the medium in which the host cells arecultured, from which medium the anti-ILT5 antibody or ILT5-bindingfragment can be recovered. Standard recombinant DNA methodologies areused to obtain antibody heavy and light chain genes, incorporate thesegenes into recombinant expression vectors, and introduce the vectorsinto host cells (e.g., methodologies such as those described inSambrook, Fritsch and Maniatis (eds), Molecular Cloning; A LaboratoryManual, Second Edition, Cold Spring Harbor, N.Y., 1989; Ausubel, F. M.et al. (eds.) Current Protocols in Molecular Biology, Greene PublishingAssociates, 1989; and in U.S. Pat. No. 4,816,397, each of which isincorporated herein by reference in its entirety.

As is understood in the art, an expression vector comprises sequencesthat mediate replication and often comprises one or more selectablemarkers. An expression vector is transfected into a host cell bystandard techniques. Non-limiting examples include electroporation,calcium-phosphate precipitation, DEAE-dextran transfection and the like.

To express an anti-ILT5 antibody or an ILT5-binding antibody fragment,DNA (e.g., cDNA) molecules encoding partial or full-length light andheavy chains (e.g., human or humanized heavy and light chains) may beinserted into expression vectors such that the genes are operativelylinked to transcriptional and translational control sequences. In thiscontext, the term “operatively linked” means that a nucleic acidsequence encoding the anti-ILT5 antibody or ILT5-binding fragment isinserted into a vector such that transcriptional and translationalcontrol sequences within the vector serve their intended function ofregulating the transcription and translation of the nucleic acidsequence. In certain embodiments, the expression vector and expressioncontrol sequences are chosen to be compatible with the expression hostcell used. Nucleic acid sequences encoding the light and heavy chainsmay be inserted into separate vectors or both genes may be inserted intothe same expression vector. The nucleic acid sequences may be insertedinto the expression vector by standard methods (e.g., ligation ofcomplementary restriction sites on the binding molecule gene fragmentand vector, or blunt end ligation if no restriction sites are present).Prior to insertion of light and/or heavy chain-encoding sequences, theexpression vector may already comprise a nucleic acid sequence encodinga constant region. For example, one approach to converting VH and VLsequences to full-length antibody-encoding sequences is to insert theminto expression vectors already encoding heavy chain constant and lightchain constant regions, respectively, such that the VH segment isoperatively linked to the CH segment(s) within the vector and the VLsegment is operatively linked to the CL segment within the vector.Additionally or alternatively, the recombinant expression vector canencode a signal peptide fused in frame to the heavy and/or light chainthat facilitates secretion of the binding molecule chain from a hostcell. The signal peptide can be an immunoglobulin signal peptide or aheterologous signal peptide (i.e., a signal peptide from anon-immunoglobulin protein).

Those skilled in the art will be able to determine whether an antibodyor fragment comprising a given polypeptide sequence binds to ILT5without undue experimentation using standard methodologies such as,without limitation, Western blots, ELISA assays, and the like.

Certain embodiments of methods and compositions provided herein arefurther illustrated by the following examples. The examples are providedfor illustrative purposes only. They are not to be construed as limitingthe scope or content of the invention in any way.

EXAMPLES Example 1 Preparation of Anti-ILT5 Antibodies

A human ILT5-mouse Ig fusion construct was generated using standardmolecular biology techniques. Soluble ILT5-Ig fusion protein waspurified from the cell culture supernatant of transiently transfected293 cells by Protein A/G-Sepharose chromatography. Expression plasmidDNA (100 μg) encoding the ILT5-Ig fusion protein was coated onto goldbeads (1 μM) according to instructions from the manufacturer (Bio-Rad,Hercules, Calif.). Mice were immunized with hILT5-Ig expressionplasmid-coated gold beads every other day for 10 days using a Helios®Gene Gun. Sera from immunized mice were tested for reactivity by ELISAagainst purified hILT5-Ig protein. Mice with demonstrated serumimmunoreactivity were boosted with recombinant hILT5-Ig fusion protein(20 μg/200 μl) three days prior to fusion. Hybridoma supernatants werescreened by ELISA for immunoreactivity against purified hILT5-Ig and anirrelevant Ig fusion protein. Hybridomas producing antibody reactivewith hILT5-Ig but not the irrelevant fusion protein were cloned bylimiting dilution and soft agar. The 8G6 mAb (IgG1,κ, hereafter referredto as “TRX585”) was purified from hybridoma culture supernatant byProtein G Sepharose column chromatography and dialyzed againstDulbecco's Phosphate Buffered Saline overnight at 2-8° C. The purifiedTRX585 mAb was stored at −80° C. until use.

Example 2 Expression of ILT5 Receptor

Surface Expression of ILT5:

Peripheral blood mononuclear cells (PBMCs) from healthy human blooddonors were stained with a murine monoclonal antibody (TRX585)comprising a heavy chain variable region comprising the amino acidsequence of SEQ ID NO: 2 or SEQ ID NO: 3, and a light chain variableregion comprising the amino acid sequence of SEQ ID NO: 1. Sequencinganalysis of the heavy chain variable region was inconclusive as towhether the first amino acid residue was D or E. As the two amino acidsare very similar and the first residue is not in a CDR, it is highlylikely that VH with D or E at the first position would have very similarif not the same ILT5-binding properties. PBMCs were also stained withantibodies specific for defined hematopoietic cell lineages and analyzedfor ILT5 expression by flow cytometry.

ILT5 Expression by CD4⁺ and CD8⁺ T Cells:

The surface expression of ILT5 was observed on about 1% of CD56⁻CD4⁺CD3⁺T cells but not on CD56⁻CD8⁺CD3⁺ T cells (FIG. 1A). Experimental detailscan be found in FIG. 1A and the description thereof.

ILT5 Expression by Tregs:

ILT5 expression by regulatory T cells (Tregs) was examined by stainingwith the TRX585 antibody. Näive Foxp3⁺CD4⁺CD3⁺ cells were found todisplay about 10 fold more ILT5 than their Foxp3− counterpart (see FIG.1B). Furthermore, 5% of CD4⁺ natural killer T (NKT) cells, anotherimmunomodulatory T cell subset that is restricted by the non-classicalMHC class I molecule, CD1d, also exhibited surface expression of ILT5(FIG. 1C). Experimental procedures can be found in FIG. 1 (panels B andC) and the description thereof.

ILT5 Expression by APCs:

ILT5 expression was measured on APCs by staining with the TRX585antibody. Steady state myeloid dendritic cells (DCs) (CD11c⁺HLA⁻DR⁺cells) showed ILT5 expression whereas plasmacytoid DCs did not expresssurface ILT5 (see FIG. 1D). In contrast, the majority of monocyticsubsets were found to express ILT5, albeit at varying levels (FIG. 1E).Further experimental details can be found in FIG. 1 (panels D, E) andthe description thereof.

ILT5 Expression by MDSCs:

Cancer patients often show an increase in myeloid-derived suppressorcells (MDSCs), which can suppress T cell responses in peripheral blood,as well as within the tumors. Increasing evidence suggests that MDSCscontribute to the induction of tolerance in cancer and some otherpathologies. ILT5 expression on steady state peripheral blood MDSCs,defined as CD33^(hi)CD34^(lo)CD11b⁺CD14⁺ cells, was detected by stainingwith the TRX585 antibody. These cells were found to express high levelsof surface ILT5 (FIG. 1F). Experimental procedures are detailed in FIG.1F and the description thereof.

Example 3 Characteristics and Biological Activity of the TRX585Anti-ILT5 Antibody

Immunoregulatory Properties of TRX585 Antibody:

Stimulation of peripheral blood mononuclear cells (PBMC) with mitomycinC-treated allogeneic PBMCs is an established in vitro model for T cellresponsiveness. Because ILT molecules are thought to beimmunomodulatory, it was tested whether crosslinking of ILT5 by means ofthe mouse anti-human ILT5 TRX585 antibody would modulate a mixedlymphocyte response (MLR). To this end, the proliferation of allogeneicPBMCs in primary MLRs performed in the presence or absence of increasingdoses of soluble TRX585 antibody or a mouse IgG1 isotype controlantibody (mIgG1) was compared. There was no change in the intensity ofthe MLR responses for varying concentrations of control mIgG1 (see FIG.2). In contrast, TRX585 antibody-mediated a dose-dependent enhancementof cell proliferation (FIG. 2). Further detail can be found in FIG. 2and the description thereof.

These observations were established under conditions in which TRX585antibody was left in the culture for the entire duration of the assay.To examine whether the TRX585 antibody-mediated increase of T cellproliferation was dependent on the level of antibodies present in theculture, ILT-expressing antigen-presenting cells (APCs) were pretreatedwith soluble (50 μg/ml) TRX585 antibody for 24-48 hours, washed, andutilized as stimulators in allogeneic MLRs. Pretreatment of monocytes orperipheral blood DCs with soluble TRX585 antibody prior to its use inMLR assays recapitulated the antibody-mediated enhancement of cellproliferation that was observed in initial experiments (FIG. 3). Furtherdetail can be found in FIG. 3 and the description thereof.

Myeloid/monocytic cells express both activation and inhibitory Fcreceptors, the engagement of which by antibodies can either enhance ordownregulate immunity and, thus, either increase or decrease the potencyof antibodies with immunoregulatory properties. To test whether thebiological effect of TRX585 antibody could be enhanced by Fccrosslinking, primary MLR assays were conducted as described above inthe presence or absence of 10 μg/ml F(ab′)₂ goat anti-mouse IgGantibody. At subsaturating concentrations (<10 μg/ml), monovalent (i.e.,in the absence of F(ab′)₂ goat anti-mouse IgG antibody) but not divalentTRX585 antibody (i.e., in the presence of F(ab′)₂ goat anti-mouse IgGantibody) induced cell proliferation (see FIG. 4). However, addition ofTRX585 antibody at concentrations higher than that of F(ab′)₂ fragmentsrestored hyperresponsiveness, albeit at levels much lower than thatobserved with identical concentrations of monovalent TRX585 antibody(i.e., in the absence of F(ab′)₂ goat anti-mouse IgG antibody) (see FIG.4). Experimental procedures are detailed in FIG. 4 and the descriptionthereof.

To determine whether the above observations could be extended toantibodies of higher valency, allogeneic PBMCs were seeded either withsoluble or solid phase TRX585 antibody. Antibody-induced proliferationwas observed with soluble but not TRX585 antibody immobilized on plastic(see FIG. 5 and the description thereof). In accordance with theseobservations, pretreatment of APCs with solid phase antibody did notlead to an enhancement of T cell responses (data not shown). Addition ofsoluble TRX585 antibody to APCs resulted in occupancy and partialinternalization of surface ILT5, whereas addition of solid phase TRX585antibody to APCs induced complete internalization of ILT5 (data notshown).

Overall, these observations indicate that monovalent and polyvalentTRX585 antibodies have a differential effect on APCs and APC-mediatedregulation of T cell responses. Furthermore, the above findings suggestthat in vivo hypercrosslinking of ILT5 antigens on APCs by TRX585antibody may decrease the effectiveness of the latter reagents.Crosslinking can be reduced by modification of the antibody to reduce oreliminate binding via the Fc receptors.

Closer examination of proliferating cells in MLR assays revealed thatTRX585 antibodies induced the proliferation of the vast majority of CD4⁺and CD8⁺ T cells in allogeneic as well as autologous settings. This wasdetermined by examining cell content CFSE dye by flow cytometry sincethis fluorescent dye gets diluted as cells divide (see FIG. 6A and thedescription thereof). In another experiment, purified T cells werecultured with the TRX585 or mIgG1, with or without allogeneic stimulatorcells. The lack of proliferation of the purified T cells, which wasobserved, ruled out the possibility that TRX585 antibody was directlymitogenic to T cells, and demonstrated that TRX585 antibody-induced Tcell proliferation required the presence of non-T cells (see FIG. 6B andthe description thereof).

Because not all T cells can undergo simultaneous proliferation as aconsequence of self and/or non-self recognition, the previousobservations suggested that TRX585 antibody-induced T cell proliferationwas achieved in a TCR-independent manner (e.g., proliferation does notrequire recognition of a MHC molecule by a TCR). Indeed, blocking TCR:MHC/peptide complex interactions by means of pan anti-MHC antibodies didnot abrogate TRX585 antibody-induced T cell proliferation (see FIG. 7).Further detail can be found in FIG. 7 and the description thereof.

Generation of T Cells with Altered Phenotype:

Upon culturing PBMCs with the TRX585 antibody as described above,proliferating CD4⁺ and CD8⁺ T cells acquired a unique phenotype. Inaddition to upregulating CD25, T cells also upregulated expression ofNKG2D, a major innate activating immune receptor that plays an importantrole in anti-tumor and anti-viral immunity (see FIGS. 8A and 8B and thedescription thereof).

Ligands for NKG2D are rarely detected on healthy tissues and cells, butare often expressed by tumor cells as well as virus-infected cells. Inhumans and mice, local as well as systemic (through shedding of NKG2Dligands) down-regulation of NKG2D as a consequence of persistentexpression of NKG2D ligands is one mechanism by which tumors and virusesescape immune surveillance. We thus examined NKG2D expression on T cellsthat were subjected to both TRX585 antibodies and signals mimickingNKG2D persistent engagement by NKG2D ligands. Remarkably, TRX585antibody-exposed T cells not only upregulated NKG2D at levels higherthan that observed on steady state natural killer (NK) cells (see FIG.8B and the description thereof for further detail), but presented with asustained expression of NKG2D under conditions that normally trigger itsinternalization and subsequent degradation (e.g., via NKG2D engagementby either soluble MICA antigen (a NKG2D ligand) or anti-NKG2D mAbs,clones 1D11 and 5C6) (see FIG. 9 and the description thereof for furtherdetail).

The tight control of NKG2D-mediated effector functions bymicroenvironmental factors, such as NKG2D ligands and cytokines, shouldprovide an additional safeguard mechanism to prevent the development ofunwanted immune responses.

Production of Cytokines and Chemokines:

Supernatants from MLR assay cultures conducted in the presence ofsoluble TRX585 antibody contained increased amounts of TNF-alpha and IL5as compared to control cultures (data not shown). Addition of TRX585antibody did not result in overproduction of other major cytokines suchas IL2, IFN-gamma, IL17, IL6, and IL12. In contrast, TRX585antibody-containing cultures contained increased amounts of Rantes,IP-10 and MIP-1 chemokines, which play an active role in recruitingleukocytes into inflammatory sites and can elicit powerful antitumoreffect in vivo (data not shown). In cultures containing TRX585 antibody,T cells also overproduced soluble Fas ligand, a factor that participatesin essential effector functions of the immune system and is, forexample, a potent mediator of cytotoxicity. Further detail can be foundin FIG. 10 and the description thereof. The above observation promptedinvestigation into whether TRX585 antibody-activated T cells wereendowed with cytotoxic activity. To this end, PBMCs were cultured in thepresence of TRX585 or mIgG1 antibodies for 3.5 days. Proliferating Tcells (effector cells) were subsequently cell-sorted and mixed with avariety of tumor cells (target cells) at different effector:target (E:T)ratios for 12-18 hours. Examination of tumor cell viability after theincubation showed that T cells from TRX585 antibody-containing but notmIgG1-containing precultures exerted a potent anti-tumor cytotoxiceffect (see FIGS. 11A and B). Although the presence of human cytotoxic Tcells has been reported in a number of viral infections and rheumatoidarthritis, acquisition of lytic activity by CD4⁺ T cells is a rareevent. Yet, preactivation of PBMCs with TRX585 antibodies was found toconfer a cytotoxic activity to both CD4⁺ and CD8⁺ T cell subsets (seeFIG. 11C and the description thereof for experimental procedures). Ofnote, the cytotoxic activity of CD4⁺ and CD8⁺ T cells appeared to bespecific to tumor cells but not healthy cells since the same T cells didnot kill autologous or allogeneic PBMCs using the same killing assay(not shown).

TRX585 antibody-induced cytotoxic CD4⁺ and CD8⁺ T cells did not expressperforin or granzyme A (data not shown), ruling out these molecules aspossible mediators of the observed cytotoxicity. In contrast, blockingMHC class I molecules or Fas ligand by means of a pan anti-MHC class Iantibody or a neutralizing anti-Fas ligand antibody, respectively,markedly diminished the anti-tumor cytotoxic effect of T cells fromTRX585 antibody-containing cultures. Further detail can be found in FIG.12 and the description thereof. In addition, both CD4⁺ and CD8⁺ T cellsfrom TRX585 antibody-containing cultures were found to express highlevels of granzyme B.

Overall, these data demonstrate that while T cells that have beencultured with APC and TRX585 antibody are able to exert a potentcytotoxic effect, such cells do not exhibit cytotoxic function in theabsence of an appropriate trigger.

To determine whether the sequence of administration of TRX585 antibodyimpacted the modulation of immune responses, we conducted a series of invitro experiments in which either TRX585 antibody and TCR stimulationwere given simultaneously, or TRX585 antibody was added prior to thedelivery of TCR stimulus. FIG. 13 shows that, while CD4⁺ and CD8⁺ Tcells from PBMC cultures containing TRX585 antibody divided actively,concomitant treatment of PBMCs with anti-CD3 and TRX585 antibodiesresulted in the inhibition of TRX585-induced T cell proliferation. Incontrast, when T cells that were induced to proliferate in TRX585antibody-containing PBMC cultures were subsequently purified andsubjected to anti-CD3 stimulation, such T cells showed markedlyincreased responsiveness to TCR stimulation and upregulated TCR:CD3complexes on the cell surface (see FIGS. 14A and 14B and the descriptionthereof for additional detail).

Overall, these results indicate that TRX585 antibody may be used toovercome tumor-specific tolerance, enhance immune responses and/orinduce tumor cell killing. Such effects may result from acquisition ofanti-tumor cytotoxic function by the T cells resulting fromadministration of TRX585 antibodies followed by another therapeuticagent or antigen.

Example 4 Use of Anti-ILT5 Antibodies and Fragments as ImmunostimulatoryAdjuvants

An anti-ILT5 antibody or an ILT5-binding antibody fragment is used as animmunostimulatory agent to enhance an immune response to an antigen ofinterest. To stimulate an antibody or cellular immune response to anantigen of interest in vivo (e.g., for vaccination purposes), theantigen and an anti-ILT5 antibody or an ILT5-binding antibody fragmentare administered to a human subject such that an enhanced immuneresponse occurs in the subject. The antigen of interest and theanti-ILT5 antibody or ILT5-binding fragment are formulatedappropriately, e.g., in separate pharmaceutical compositions. In certainsituations, it may be desirable to administer the antibody at or aboutthe same time as the antigen. In certain situations, it may be desirableto administer the antibody first, followed by the antigen, wherein apriming dose of the antibody is administered prior to administration ofthe antigen of interest to allow pharmacodynamic effect on the T-cells.For example, the anti-ILT5 antibody or ILT5-binding fragment can beadministered 1-14 days (e.g., 3 days) before administration of theantigen of interest. It is expected that upon administration of theantigen of interest, a robust immune response against the antigen willbe induced.

Example 5 Use of Anti-ILT5 Antibodies and Fragments to Increase aSpecific Immune Response to Tumor Cells

An anti-ILT5 antibody or an ILT5-binding antibody fragment isadministered to a subject having tumor cells to overcome tumor-specifictolerance in the subject and to upmodulate an immune response to inhibittumor growth, metastasis or to trigger tumor eradication. The tumor maybe, for example, of the hematopoietic system, such as, a leukemia,lymphoma, or other malignancy of blood cells, or of a solid tumor, suchas, a melanoma, gastric, lung, breast, and prostate cancers. In certainembodiments, such anti-ILT5 antibodies or ILT5-binding fragments areused as part of a combination therapy with another therapeutic treatmentin a subject as adjuvants used to enhance an immune response such as incombination with chemotherapeutic agents. It is expected that uponadministration of the anti-ILT5 antibody or ILT5-binding fragmentthereof, tumor-specific tolerance will be reduced, resulting indiminished tumor growth or metastasis, and tumors will be eradicated orreduced in size or number. Following administration of the anti-ILT5antibody, one or more appropriate tumor antigens (see above) or vaccinesmay also be administered.

Example 6 Use of Anti-ILT5 Antibodies and Fragments to Increase aSpecific Immune Response to Cells Infected with a Virus

An anti-ILT5 antibody or an ILT5-binding antibody fragment isadministered to a subject suffering from a viral infection to upmodulatean immune response against cells infected with the virus. In certainembodiments, such anti-ILT5 antibodies or ILT5-binding fragments areused as part of a combination therapy with another therapeutic treatmentin a subject as adjuvants used to enhance an immune response. It isexpected that upon administration of the anti-ILT5 antibody orILT5-binding fragment thereof, cells infected with the virus areeliminated or reduced in number. Following administration of theanti-ILT5 antibody, one or more appropriate viral antigens (see above)or vaccines may also be administered.

Example 7 Use of Crosslinked or Aggregated Anti-ILT5 Antibodies andFragments to Induce Tolerance

A crosslinked or otherwise aggregated anti-ILT5 antibody or anILT5-binding antibody fragment is administered to a subject to inhibit acellular immune response to an antigen of interest in vivo. Withoutwishing to be bound by theory, it is hypothesized that co-engagement ofILT5 receptors by such crosslinked, but not monovalent, anti-ILT5antibodies and ILT5-binding fragments, initiates an inhibitory cascadein ILT-expressing APCs, which decreases their stimulatory potential ormight render them tolerogenic. In certain embodiments, a crosslinked orotherwise aggregated anti-ILT5 antibody or ILT5-binding fragment may beadministered at the same time as administration of another therapeuticagent or antigen to inhibit immune response to the antigen. It will beappreciated that the effects of concomitant removal of ILTligand-transduced inhibitory signals in T cells and decreasedDC-immunostimulatory capacities counterbalance each other and lead todiminished immunity. It is expected that upon administration of theanti-ILT5 antibody or ILT5-binding fragment thereof, tolerance will beinduced.

Procedures such as those described in Example 6 would be useful astreatments of, for example, autoimmune diseases and immunologicalrejection of allogeneic and xenogeneic organ, tissue, or celltransplants.

What is claimed is:
 1. An isolated antibody or an antigen bindingfragment thereof that binds human immunoglobulin-like transcript 5(ILT5) comprising: a heavy chain complementarity determining region 1(VH CDR1) comprising the amino acid sequence of SEQ ID NO: 4; a heavychain complementarity determining region 2 (VH CDR2) comprising theamino acid sequence of SEQ ID NO: 5; a heavy chain complementaritydetermining region 3 (VH CDR3) comprising the amino acid sequence of SEQID NO: 6; a light chain complementarity determining region 1 (VL CDR1)comprising the amino acid sequence of SEQ ID NO: 7; a light chaincomplementarity determining region 2 (VL CDR2) comprising the amino acidsequence of SEQ ID NO: 8; and a light chain complementarity determiningregion 3 (VL CDR3) comprising the amino acid sequence of SEQ ID NO: 9.2. The isolated antibody or fragment of claim 1, further comprising atleast one human framework region.
 3. The isolated antibody or fragmentof claim 2, wherein the human framework region is a human heavy chainframework region.
 4. The isolated antibody or fragment of claim 3,comprising one or more human heavy chain framework regions from a heavychain variable region comprising an amino acid sequence selected fromthe group consisting of the amino acid sequence of SEQ ID NO: 10, SEQ IDNO: 11, SEQ ID NO: 12, SEQ ID NO: 13, SEQ ID NO: 14, SEQ ID NO: 15, SEQID NO: 16, and SEQ ID NO:
 17. 5. The isolated antibody or fragment ofclaim 2, wherein the human framework region is a human light chainframework region.
 6. The isolated antibody or fragment of claim 5,comprising one or more human light chain framework regions from a lightchain variable region comprising an amino acid sequence selected fromthe group consisting of the amino acid sequence of SEQ ID NO: 18, SEQ IDNO: 19, SEQ ID NO: 20, SEQ ID NO: 21, SEQ ID NO: 22, SEQ ID NO: 23, andSEQ ID NO:
 24. 7. The isolated antibody or fragment of claim 6,comprising one or more human heavy chain framework regions from a heavychain variable region comprising an amino acid sequence selected fromthe group consisting of the amino acid sequence of SEQ ID NO: 10, SEQ IDNO: 11, SEQ ID NO: 12, SEQ ID NO: 13, SEQ ID NO: 14, SEQ ID NO: 15, SEQID NO: 16, and SEQ ID NO:
 17. 8. The isolated antibody or fragment ofclaim 1, comprising a heavy chain constant region.
 9. The isolatedantibody or fragment of claim 8, wherein the heavy chain constant regionis selected from the group consisting of: an IgG1 constant region, anIgG2 constant region, an IgG3 constant region, an IgG4 constant region,an IgA constant region, an IgE constant region, an IgM constant region,and an IgD constant region.
 10. The isolated antibody or fragment ofclaim 8, wherein the heavy chain constant region is an IgG1 constantregion.
 11. The isolated antibody or fragment claim 8, wherein the heavychain constant region comprises the amino acid sequence of SEQ ID NO: 25or SEQ ID NO:
 26. 12. The isolated antibody or fragment of claim 1,comprising a light chain constant region.
 13. The isolated antibody orfragment of claim 12, wherein the light chain constant region is a kappalight chain constant region.
 14. The isolated antibody or fragment ofclaim 12, wherein the light chain constant region is a lambda lightchain constant region.
 15. The isolated antibody or fragment claim 12,wherein the light chain constant region comprises the amino acidsequence of SEQ ID NO:
 27. 16. The isolated antibody or fragment ofclaim 1, comprising a light chain comprising the amino acid sequence ofSEQ ID NO:
 28. 17. The isolated antibody or fragment of claim 16,further comprising a heavy chain comprising the amino acid sequence ofSEQ ID NO: 29, SEQ ID NO: 30, SEQ ID NO: 31, or SEQ ID NO:
 32. 18. Theisolated antibody or fragment of claim claim 1, comprising a heavy chaincomprising the amino acid sequence of SEQ ID NO: 29, SEQ ID NO: 30, SEQID NO: 31, or SEQ ID NO:
 32. 19. The isolated antibody or fragment ofclaim 1, comprising a light chain variable region comprising the aminoacid sequence of SEQ ID NO:
 1. 20. The isolated antibody or fragment ofclaim 1, comprising a heavy chain variable region comprising the aminoacid sequence of SEQ ID NO: 2 or SEQ ID NO:
 3. 21. The isolated antibodyor fragment of claim 1, comprising a light chain variable regioncomprising the amino acid sequence of SEQ ID NO: 1, and furthercomprising a heavy chain variable region comprising the amino acidsequence of SEQ ID NO: 2 or SEQ ID NO:
 3. 22. An antigen bindingfragment of claim 1, wherein the fragment comprises a Fab fragment, aF(ab′)2 fragment, or a scFv fragment.